Loss of heterozygosity (LOH) at chromosomal loci has been associated with the presence of tumor suppressor genes at the deleted loci. Twenty-six clinically localized, Stage B prostate carcinomas were analyzed for LOH on chromosomes 10 and 17 using microsatellite markers. Two of 26 carcinomas showed LOH on 17p while one showed LOH on 17q. Chromosome 10 showed a complex pattern of LOH with monosomy (1 case), LOH on 10p (1 case), proximal 10q (1 case) and distal 10q (2 cases). Overall 29% of informative cases showed LOH on chromosome 10. These results are consistent with the presence of a tumor suppressor for prostate cancer on 17p and multiple tumor suppressor genes on chromosome 10.