The murine mAb F77, IgG3 subtype, was raised against the prostate cancer cell line PC3 (5, 6) and found to recognize both androgen-independent (PC3, PC3-MM2, and DU 145) and androgen-dependent (LNCaP) human prostate cancer cells, with little or no binding to nonprostatic cells. This evidence concerns the gene IGHG3 and Familial prostate cancer.