OBJECTIVE We have previously developed methods for the quantification of different macromolecules in aspiration biopsy material and described the changes in prostate-specific antigen (T-PSA) during cancer treatment. We have now studied the changes in tissue prostatic acidic phosphatase (T-PAP) in 58 endocrine-treated patients with prostatic carcinoma and compared these data with cancer development data and tissue PSA (T-PSA) levels. METHODS PAP and PSA were quantified in aspiration biopsies taken before treatment and after 6 and 12 months of treatment. Patients were followed until death or for >98 months. RESULTS Pretreatment T-PSA was more strongly associated with survival than T-PAP. Both T-PSA and T-PAP decreased in responders during treatment. In non-responders, T-PSA and T-PAP increased after 12 months in 17/18 and 7/13 patients, respectively. Estrogen-treated responders had significantly higher T-PSA, but not T-PAP, treatment values than those treated with orchidectomy or gonadotropin-releasing hormone. CONCLUSIONS The inferiority of serum PAP compared to PSA for monitoring cancer treatment may reflect its less pronounced changes at the tissue level, indicating different in vivo regulation of the two markers. Estrogen stimulation of PSA synthesis in vivo may underlie the higher PSA levels observed during estrogen treatment.