The human sex-region Y (SRY) gene maps to Yp11.3 and encodes a protein that shares significant sequence homology with a conserved DNA binding motif found in the nonhistone high-mobility group (HMG) proteins. In the mouse, Sry is required for normal testicular development and is expressed in the developing male gonadal ridge as well as in the adult testis. In man, SRY expression has been observed in the adult testis, but not in other adult male tissues. We have analyzed samples from human prostate adenocarcinoma and benign prostatic hypertrophy (BPH) for the expression of the SRY gene. We found expression of SRY in 60% of malignant prostate tumors and in three of six samples of BPH. We did not find expression in male or female colon mucosa, or in tissue from a cystic ovary. Malignant and atrophic testicular tissue both contained SRY transcript and served as positive controls in these experiments. We also found SRY transcript in the DU-145 prostate adenocarcinoma cell line. Interestingly, SRY expression is absent in the Tera-2 teratocarcinoma cell line. The potential for the SRY gene product to bind HMG core response elements in vitro suggests that SRY could participate in the cascade of gene regulatory events that result in aberrant cell growth or malignancy.