Prostate cancer is one of the most common malignancies in men. Few authors have attempted to identify consistent genetic alterations at the molecular level in adenocarcinoma of the prostate, but those most frequently reported are loss of heterozygosity (LOH) involving chromosome arms 8p, 10q, 16q, and 18q and inactivation of the TP53 tumor suppressor gene. In order to determine if alterations frequently found in other adenocarcinomas (breast, ovarian, colorectal), including losses of genetic material from chromosome arms 1p, 3p, 7q, 8p, 11p, 17p, 17q, and 18q, are also involved in prostate cancer, we examined 20 localized early-stage prostate tumors. We detected no mutations of the TP53 gene. Allelic losses were found from 7q (33%), 8p (50%), 10q (20%), and 18q (33%). Furthermore, as the first step toward isolating tumor suppressor genes on 18q, we used six polymorphic markers and identified a small common deleted region between the chromosome 18 centromere and the D18S19 locus.