Serum prostatic specific antigen (PA) and prostatic acid phosphatase (PAP) levels were measured in 113 untreated patients with prostatic cancer and in 137 patients with benign prostatic hypertrophy (BPH). Of the 113 cancer patients, 81% and 69%, respectively, were detectable by means of PA or PAP assay alone. PA was a more sensitive indicator, than PAP in all stages, especially localized disease (stages A, B and C). Using the BPH group as a negative control, specificities of PA and PAP were 81% and 94% respectively. In another group of 68 patients with BPH whose blood samples were taken immediately after prostatic manipulation, both PA and PAP levels were elevated significantly. In 87 of the 113 cancer patients the two markers were serially determined, and 22 patients presented disease progression. Concerning the sensitivity within 6 months before progression, PA appears to be more reliable than PAP in early detection of disease progression. According to Kaplan-Meier projections, the patients with normal pretreatment PA levels had significantly longer intervals to progression than did those with moderate to marked PA elevation (more than 100 ng/ml) (P less than 0.05). This study shows that PA is more reliable than PAP for detection and monitoring of prostatic cancer. Pretreatment PA levels appear to be of a high prognostic value for time to progression, irrespective of stage and treatment regimen.