Eighteen patients with prostatic adenocarcinoma, treated with oestrogen for 45 months or more, were followed-up after withdrawal of oestrogen treatment. Serum concentrations of testosterone, luteinizing hormone (LH), follicle-stimulating hormone (FSH), oestradiol-17 beta, testosterone-oestradiol-binding globulin (TeBg) and prolactin were measured at different intervals between 3 and 42 months after cessation of treatment. Serum testosterone concentrations after cessation of oestrogen treatment were low (range 71.4 +/- 6.3 to 120.8 +/- 23.7 nmol/100ml), whereas the concentrations of LH (range 21.8 +/- 3.6 to 32.6 +/- 9.1 U/1) and FSH (range 31.2 +/- 5.5 to 54.7 +/- 9.5 U/1) were within or higher than the reference range. Prolactin (range 6.0 +/- 85.3 to 7.9 +/- 68.2 micrograms/1) was within the reference range. No significant changes in serum concentrations of testosterone, LH, FSH and prolactin occurred during the follow-up period. The serum concentrations of both oestradiol-17 beta and TeBg, found between 13 and 36 months after oestrogen cessation (range 43.8 +/- 4.6 to 46.2 +/- 5.9 and 64.0 +/- 2.5 to 86.0 +/- 10.0, respectively) were significantly lower than the concentrations found between 3 and 12 months (range 71.9 +/- 10.4 to 99.8 +/- 12.9 and 124.1 +/- 15.5 to 140.2 +/- 13.7, respectively). It is concluded that in patients with prostatic adenocarcinoma, long-term oestrogen treatment causes an irreversible impairment of Leydig cell function and consequently a reduced testosterone secretion after cessation of oestrogen treatment.