diff --git a/spellchecker/utils.py b/spellchecker/utils.py
index 437a7aa..7260d42 100644
--- a/spellchecker/utils.py
+++ b/spellchecker/utils.py
@@ -1,8 +1,8 @@
 """ Additional utility functions """
 import contextlib
 import gzip
-import re
 import functools
+import re
 import warnings
 
 from .info import __version__
@@ -135,4 +135,4 @@ def _parse_into_words(text):
             text (str): The text to split into words
     """
     # see: https://stackoverflow.com/a/12705513
-    return re.findall(r"(\w[\w']*\w|\w)", text.lower())
+    return re.findall(r"(\w[\w']*\w|\w)", text)

diff --git a/tests/spellchecker_test.py b/tests/spellchecker_test.py
index bf13fa4..772ac1b 100644
--- a/tests/spellchecker_test.py
+++ b/tests/spellchecker_test.py
@@ -36,13 +36,13 @@ class TestSpellChecker(unittest.TestCase):
     def test_words(self):
         ''' test the parsing of words '''
         spell = SpellChecker()
-        res = ['this', 'is', 'a', 'test', 'of', 'this']
+        res = ['This', 'is', 'a', 'test', 'of', 'this']
         self.assertEqual(spell.split_words('This is a test of this'), res)
 
     def test_words_more_complete(self):
         ''' test the parsing of words '''
         spell = SpellChecker()
-        res = ['this', 'is', 'a', 'test', 'of', 'the', 'word', 'parser', 'it', 'should', 'work', 'correctly']
+        res = ['This', 'is', 'a', 'test', 'of', 'the', 'word', 'parser', 'It', 'should', 'work', 'correctly']
         self.assertEqual(spell.split_words('This is a test of the word parser. It should work correctly!!!'), res)
 
     def test_word_frequency(self):
@@ -413,7 +413,7 @@ class TestSpellChecker(unittest.TestCase):
         ''' test using split_words '''
         spell = SpellChecker()
         res = spell.split_words("This isn't a good test, but it is a test!!!!")
-        self.assertEqual(set(res), set(["this", "isn't", "a", "good", "test", "but", "it", "is", "a", "test"]))
+        self.assertEqual(set(res), set(["This", "isn't", "a", "good", "test", "but", "it", "is", "a", "test"]))
 
     def test_iter_spellchecker(self):
         """ Test using the iterator on the SpellChecker """
@@ -440,3 +440,17 @@ class TestSpellChecker(unittest.TestCase):
             self.assertTrue(word in spell)
             cnt += 1
         self.assertEqual(cnt, len(spell.word_frequency.dictionary))
+
+    def test_case_sensitive_parse_words(self):
+        """ Test using the parse words to generate a case sensitive dict """
+        spell = SpellChecker(language=None, case_sensitive=True)
+        spell.word_frequency.load_text("This is a Test of the test!")
+        self.assertTrue("This" in spell)
+        self.assertFalse("this" in spell)
+
+    def test_case_insensitive_parse_words(self):
+        """ Test using the parse words to generate a case insensitive dict """
+        spell = SpellChecker(language=None, case_sensitive=False)
+        spell.word_frequency.load_text("This is a Test of the test!")
+        # in makes sure it is lower case in this instance
+        self.assertTrue("this" in spell)

Case Sensitive bug
Case sensitive parameter has no affect bcz in "_parse_into_words" method text is made lower irrespective of case sensitive parameter, need to avoid it to make case-sensitive valid
tests/spellchecker_test.py::TestSpellChecker::test_case_sensitive_parse_words tests/spellchecker_test.py::TestSpellChecker::test_split_words tests/spellchecker_test.py::TestSpellChecker::test_words tests/spellchecker_test.py::TestSpellChecker::test_words_more_complete
tests/spellchecker_test.py::TestSpellChecker::test_add_word tests/spellchecker_test.py::TestSpellChecker::test_adding_unicode tests/spellchecker_test.py::TestSpellChecker::test_bytes_input tests/spellchecker_test.py::TestSpellChecker::test_candidates tests/spellchecker_test.py::TestSpellChecker::test_capitalization_when_case_sensitive_defaults_to_false tests/spellchecker_test.py::TestSpellChecker::test_capitalization_when_case_sensitive_true tests/spellchecker_test.py::TestSpellChecker::test_capitalization_when_language_set tests/spellchecker_test.py::TestSpellChecker::test_case_insensitive_parse_words tests/spellchecker_test.py::TestSpellChecker::test_checking_odd_word tests/spellchecker_test.py::TestSpellChecker::test_correction tests/spellchecker_test.py::TestSpellChecker::test_edit_distance_invalud tests/spellchecker_test.py::TestSpellChecker::test_edit_distance_one tests/spellchecker_test.py::TestSpellChecker::test_edit_distance_one_property tests/spellchecker_test.py::TestSpellChecker::test_edit_distance_two tests/spellchecker_test.py::TestSpellChecker::test_extremely_large_words tests/spellchecker_test.py::TestSpellChecker::test_import_export_gzip tests/spellchecker_test.py::TestSpellChecker::test_import_export_json tests/spellchecker_test.py::TestSpellChecker::test_iter_spellchecker tests/spellchecker_test.py::TestSpellChecker::test_iter_word_frequency tests/spellchecker_test.py::TestSpellChecker::test_large_words tests/spellchecker_test.py::TestSpellChecker::test_load_external_dictionary tests/spellchecker_test.py::TestSpellChecker::test_load_text_file tests/spellchecker_test.py::TestSpellChecker::test_missing_dictionary tests/spellchecker_test.py::TestSpellChecker::test_pop tests/spellchecker_test.py::TestSpellChecker::test_pop_default tests/spellchecker_test.py::TestSpellChecker::test_remove_by_threshold tests/spellchecker_test.py::TestSpellChecker::test_remove_by_threshold_using_items tests/spellchecker_test.py::TestSpellChecker::test_remove_word tests/spellchecker_test.py::TestSpellChecker::test_remove_words tests/spellchecker_test.py::TestSpellChecker::test_spanish_dict tests/spellchecker_test.py::TestSpellChecker::test_tokenizer_file tests/spellchecker_test.py::TestSpellChecker::test_tokenizer_provided tests/spellchecker_test.py::TestSpellChecker::test_unique_words tests/spellchecker_test.py::TestSpellChecker::test_unknown_words tests/spellchecker_test.py::TestSpellChecker::test_word_contains tests/spellchecker_test.py::TestSpellChecker::test_word_frequency tests/spellchecker_test.py::TestSpellChecker::test_word_in tests/spellchecker_test.py::TestSpellChecker::test_word_known tests/spellchecker_test.py::TestSpellChecker::test_word_probability_calc tests/spellchecker_test.py::TestSpellChecker::test_word_usage_frequency