Prostate-specific antigen (PSA) and DNA ploidy as measured by flow cytometry were compared with conventional prognostic indicators in 112 patients who underwent radical prostatectomy for clinically resectable prostate cancer. The variables examined included age, race, prostatic acid phosphatase (PAP), Gleason score of the radical prostatectomy specimen, and pathologic stage. No significant relationships were found between DNA ploidy and age, mean PAP value, and absolute PAP value. Of the 112 patients, 65 (58.0%) had disease limited to the prostate (pathologic Stages A and B); 47 (42.0%) had extraprostatic disease (pathologic Stages C and D1). The stage was related to the Gleason score (P less than 0.0001) where extraprostatic disease was associated with a Gleason score of 6 to 10. Nineteen (17.0%) patients had aneuploid tumors, and 93 (83.0%) had diploid tumors. DNA ploidy significantly correlated with pathologic stage (P = 0.04); aneuploidy was identified more frequently in patients with Stages C and D1 tumors. Aneuploid tumors occurred more frequently than diploid tumors in patients with a Gleason score of 6 to 10 (P = 0.034). Mean PSA values were higher in patients with aneuploid tumors (P = 0.078), extraprostatic neoplasms (P = 0.00001), and cancers with a Gleason score of 6 to 10 (P = 0.0004). Furthermore, PSA values greater than 10.0 ng/ml were associated with extraprostatic disease and a Gleason score of 6 to 10 (P less than 0.05 and P less than 0.001, respectively). Significant racial differences were found with respect to DNA ploidy, mean DNA indices, and mean PSA values. The 18 black patients had more DNA aneuploid tumors (P = 0.043), a higher mean DNA index (P = 0.017), and a higher mean PSA value (P = 0.043) than the 94 white patients. Both PSA and DNA ploidy analysis by flow cytometry appear to be valuable indicators in the evaluation of patients with prostatic carcinoma.