In patients treated for prostatic carcinoma with oestrogen, orchiectomy or external radiation, serum concentrations of testosterone, LH, FSH, prolactin, TeBG and oestradiol-17 beta as well as changes in sexual behaviour and mental mood were studied. Oestrogen treatment as well as orchiectomy reduced serum testosterone concentration to similar values. Neither totally nor subcapsularly orchiectomized patients responded to HCG stimulation. The free testosterone was 68% lower in oestrogen treated than in orchiectomized patients, probably due to a high TeBG concentration induced by oestrogens. patients oestrogen treated for less than 3 years and in whom the treatment had been withdrawn had normal serum testosterone and LH at follow-up. In contrast, low serum testosterone concentration and normal LH were found after oestrogen cessation in patients oestrogen treated for more than 3 years indicating reduced Leydig cell, and/or hypothalamic-hypophyseal function. In patients oestrogen treated for more than 3 years the serum testosterone concentration neither increased after oestrogen cessation nor decreased after orchiectomy. Absorbed testes doses during radiation treatment were measured from a few to more than 10 Gy but were reduced by about 50% if the gonads were protected by lead shields during anterior and posterior treatment sessions. Radiation may affect gonadal function as decreased serum testosterone concentration and increased LH, FSH were found after treatment. Sexual function was altered after oestrogen, orchiectomy and radiation treatment. Sexual activity and capability were distinctly better maintained after radiation than after orchiectomy or oestrogen treatment. Sixty-seven percent of the patients had coitus or masturbated after radiation treatment, all experiencing orgasm. Patients on oestrogen treatment or after orchiectomy had coitus/masturbation less often (17% in both groups). They also experienced orgasm less often (8% and 17% respectively). The group of patients on oestrogen treatment had a higher average score for depression than those treated with orchiectomy or radiation treatment.