snRNAs with properties closely related to those of the major vertebrate U-snRNAs are present in the fungi Aspergillus nidulans, Neurospora crassa and Schizosaccharomyces pombe. These RNAs possess a tri-methyl guanosine cap structure and a subset cross-hybridizes with human U1 and U2 clones. In the form of snRNPs, snRNAs from these fungi as well as from Saccharomyces cerevisiae and pea plants are immunoprecipitated by human and anti-Sm or anti-(U1)RNP autoimmune antibodies. On micro-injection into the cytoplasm of Xenopus oocytes, the snRNAs are packaged into ribonucleoprotein particles and migrate into the nucleus. The results demonstrate a hitherto unsuspected degree of evolutionary conservation in snRNA structure, snRNP protein structure, and sites of RNA-protein interaction within snRNPs.