 His interest in the dialects of border areas led him to the study of East Slovak and Ukrainian dialects, where his work focused on toponyms, their etymology, and the history and settlement of the places where they are attested.He also carried out research on Sorbian and Belarusian, and was involved in producing linguistic atlases of Kashubian (1964–78), Polish (Nitsch 1957-70), and Lemkian (1956–64).Particularly valuable was his introduction of colors and symbols to dialect maps.