A partial-length cDNA encoding a cell death-associated gene designated RP-8 was cloned from rat thymocytes by Owens and co-workers (Mol. Cell. Biol. 11, 4177-4188, 1991). They reported that transcription of RP-8 was induced when rat thymocytes were caused to undergo apoptosis triggered by either radiation or treatment with dexamethasone. To study the role of RP-8 in cell death in the mouse, we have cloned a full-length mouse RP-8 cDNA from a mouse thymus cDNA library. The mouse RP-8 gene encodes of protein of 343 amino acids with 92% amino acid identity to the rat RP-8 protein. Expression of mouse RP-8 was not altered in a factor-dependent myeloid line induced to undergo apoptosis by growth factor withdrawal, or when a lymphoid cell line was triggered to undergo apoptosis by irradiation. Although these data do not prove that RP-8 is not a cell death gene, they show that RP-8 expression is not sufficient for apoptosis, and that transcriptional up regulation of RP-8 is not universally associated with apoptosis.