Nascent premessenger RNA transcripts are packaged into heterogeneous nuclear ribonucleoprotein (hnRNP) complexes containing specific nuclear proteins, the hnRNP proteins. The A and B group proteins constitute a major class of small basic proteins found in mammalian hnRNP complexes. We have previously characterized the Drosophila melanogaster Hrb98DE gene, which is alternatively spliced to encode four protein isoforms closely related to the A and B proteins. We report here that the Drosophila genome contains a family of genes related to the Hrb98DE gene. One member of the family, Hrb87F, is very homologous to Hrb98DE in both sequence and structure. The Hrb87F transcripts (1.7 and 2.2 kb) utilize two alternative polyadenylation sites, are abundant in ovaries and early embryos, and are present in lesser amounts throughout development. In one wildtype strain of Drosophila there is a naturally-occurring polymorphism in this gene due to the insertion of a 412 transposable element in the 3' untranslated region. The larger transcript is not produced in these files and thus is not required for viability. Sequence identities among the Drosophila Hrb proteins and the vertebrate A and B hnRNP proteins suggest that these proteins may form a distinct subfamily within the larger family of related RNA binding proteins.