Recently, a specific chromosome abnormality, t(X;1)(p11;q21), was described for a subgroup of human papillary renal cell carcinomas. The translocation breakpoint in Xp11 is located in the same region as that in t(X;18)(p11;q11)-positive synovial sarcoma. We used fluorescence in situ hybridization (FISH) and somatic cell hybridization techniques to demonstrate 1) that the Xp11 translocation breakpoint in papillary renal cell carcinoma differs from that observed in synovial sarcoma and has a more proximal location, and 2) that an ornithine aminotransferase (OAT)L2 containing yeast artificial chromosome (YAC) spans the X;1 translocation. This YAC provides an ideal starting point from which the breakpoint itself and the gene(s) involved can be isolated and characterized.