Of 102 patients suffering from prostatic carcinoma, complete data on the serum concentration of 7 tumour markers were available from 90 patients, together with tumour grade, local stage and the presence or absence of skeletal metastases. The serum content of prostatic acid phosphatase, prostate specific antigen, neopterin, thymidine kinase, osteocalcin, C-reactive protein and tissue polypeptide antigen was measured. By means of Cox's regression and multivariate analysis the ability of these variables to predict prognosis, i.e. death from prostatic cancer, was studied. Neopterin appeared to be the most efficient marker, followed by tumour grade, thymidine kinase and prostate specific antigen. No other variable provided information of statistical significance. In multivariate analysis thymidine kinase performed best, followed by neopterin, tumour grade and prostate specific antigen. Several serum tumour markers reflect the biological activity of human prostate cancers and their value should be further explored. They may become useful in the management of individual patients.