We investigated the localization of small molecular weight nuclear RNA (snRNA) in nuclei from avian erythrocytes, bone marrow cells, reticulocytes and liver cells. There was no qualitative difference in the existence of snRNA species (4S, 4.5S, 5S, U1, U2 and U3) between transcriptionally active and inactive cells. Polyacrylamide gel electrophoresis revealed that isolated euchromatin contained 4S, 4.5S, 5S, U1 and U2 species, while heterochromatin did only 5S and U3 RNAs. Quantitation of such snRNA species in active and inactive cell nuclei showed that amounts of 4.5S, U1 and U2 species localizing in euchromatin were remarkably constant in both kinds of cells, suggesting their possible role in either preserving euchromatin or regulating extranucleolar RNA synthesis.