Antibody-dependent cell-mediated cytotoxkity (ADCC) was used to detect HLA-A, -B and -C antigens on in vitro cultured urothelial cells of normal or malignant derivation. Alloantisera induced specific lysis of 51Cr-labelted targets by effector lymphoid cells from non-immune donors. HLA antisera were routinely titred to dilutions ≧ 10−3 on urothelial cells in primary or long-term culture. The HLA phenotype was compared for lymphoid cells and urothelial cells from eight individuals. HLA antigens detected by complement mediated lymphocytotoxkity were also detected on urothelial cells. No deletions or gains in HLA antigens were found on normal or malignant urothelial cultures as compared with donor lymphocyte HLA typings. The results show that the established urothelial cells lines J82, TCCSuP and SCaBER have retained their donor HLA phenotype. The established cell lines T24 and RT4 derived from transitional cell carcinomas and HCV-29 from urothelium were found to have distinctive HLA profiles although donor lymphocytes were not available for comparison. The serological crossreactions seen in complement mediated lymphocytotoxidty were clearly observed in ADCC. In particular, HLA-Cw5 was found to crossreact with HLA-Cw8. HLA-Cw5 was detected on 6/8 cultures of transitional cell carcinomas and this was confirmed by absorption analysis.