The Ro autoantigen is a mammalian cellular ribonucleoprotein (RNP) of unknown function. We have demonstrated that hY1 and hY4 Ro RNAs are associated with erythrocyte Ro RNPs and represent a subset of the four hY RNAs found in HeLa cell and leukocyte Ro RNPs. We have cloned and sequenced hY4 RNA, the only hY RNA not sequenced previously, from a polymerase chain reaction amplified erythrocyte hY cDNA library. Sequencing of the erythrocyte hY RNAs in conjunction with Northern blot analysis confirms that the erythrocyte hY RNAs contain the same sequences as the respective HeLa cell RNAs of similar mobility. Ribonuclease inhibition activity has been found in erythrocytes and this activity inhibits the degradation of hY3 and hY5 in leukocyte lysates thereby favoring the possibility that the presence of hY1 and hY4 in erythrocytes is the result of differential expression of the hY RNAs in erythrocyte precursors.