A total of 83 prostate adenocarcinomas was evaluated for allelic loss on chromosome 10 by analysis of loss of polymorphic microsatellite repeats. Initially, 64 stage B carcinomas were analyzed at 12 loci on chromosome 10. Nine cases showed loss of chromosome 10 sequences, with a fractional allelic loss of 20%. These nine cases were then analyzed at an additional 19 loci to define better the regions of loss. Four areas of loss were identified, including 10p (2 of 64 cases), 10q23.1 (7 of 64 cases), 10q23.3 (4 of 64 cases), and 10q26 (2 of 64 cases). Three loci in these regions, D10S111, D10S185, and D10S192, were then analyzed in 19 advanced (stage C and D) carcinomas. Seven (37%) of 19 advanced carcinomas showed allelic loss at one or more of these loci. A statistically significant increase in the fractional allelic loss at both D10S111 (10p) and D10S185 (10q23.1) was observed. Thus, a complex pattern of loss is seen on chromosome 10 in prostate carcinoma, with regions of loss on 10p and 10q, and such loss occurs at a higher rate in clinically advanced disease.