Pretreatment hormone levels were determined in 222 patients with prostatic cancer and their prognostic value assessed. The patients were grouped into yearly survival categories and only those whose cause of death was due to the disease were included in the study. Low concentrations of testosterone in plasma at the time of diagnosis related to a poor prognosis. Patients who died within 1 yr of diagnosis had the lowest mean plasma levels of this steroid. The pretreatment mean plasma testosterone concentrations were found to be higher as the survival period of the various groups lengthened. This relationship was observed both when the total data were analysed and also when the patients were subgrouped depending on clinical evidence of spread of the tumour beyond the prostatic capsule (T3) or on the presence of metastases (M1). High pretreatment plasma concentrations of luteinizing hormone were also associated with poor survival. Follicle-stimulating hormone, prolactin and growth hormone concentrations did not correlate with survival time. The indications from this study are that poor testicular function is associated with early death from prostatic carcinoma and that the measurement of blood levels of testosterone at diagnosis could provide a prognosis of subsequent life-span.