Prostate tumour markers and differentiation grade in prostatic cancer. Serum acid phosphatase activity, prostate specific phosphatase and prostate specific antigen were measured in 100 patients with prostatic cancer. The patients were divided according to the differentiation grade into 3 groups: G1 (well), G2 (moderately) and G3 (poorly differentiated) carcinoma. Bone metastases were identified by scintigraphy. Among the 76 M0 patients the mean levels of all 3 markers were slightly higher in patients with moderately differentiated prostatic carcinoma. Among the 24 M1 patients the primary tumour was either G2 (18 patients) or G3 (6 patients); none had G1 lesions. Significantly higher serum ACP and PAP levels were found in patients with G2 tumours than in those with G3 lesions. It was concluded that the histological differentiation grade of prostatic carcinoma did affect serum levels of prostatic tumour markers; the tendency towards higher levels in the G2 group was noticeable in both non-metastatic and metastatic cases despite the limited number of patients in the latter category. In clinical practice this information may be an important additional tool in staging prostatic cancer. 