Prostate-specific antigen (PSA) and prostatic acid phosphatase (PAP) have been evaluated in patients with prostatic cancer. All patients, who participated in a phase III trial (n = 110), had disseminated disease and received first line endocrine treatment of either orchidectomy or a monthly injection of a depot luteinizing hormone-releasing hormone analogue (Zoladex). Serum samples were analyzed for PSA and PAP at 0, 3, 6, and 12 months and patients were clinically assessed at 6 and 12 months. At diagnosis, 72 and 97% of all patients had elevated PAP and PSA concentrations (greater than 4 ng/ml), respectively. Patients with progressive disease had significantly higher PSA and PAP levels at both assessments. A small number of patients in the "complete remission" group had both PSA and PAP levels within the normal range after 3 months of treatment. Similarly, both PSA and PAP levels steadily declined in the group of patients who had partial regression of the disease. The patients with stable disease, however, had a significant rise only in their PSA levels at the 12-month assessment. This data suggest that PSA is more sensitive than PAP in those patients who have a "slow progression" of the disease.