Twentyone young female patients are described who presented with amenorrhoea, galactorrhoea or infertility, and were treated by 90Y pituitary implantation of 20 000 rads. There was no morbidity. In all patients serum prolactin values were elevated and radiographs of the pituitary fossa were abnormal. Observations are available for 1–76 months (mean 27) after implantation. The median fall in prolactin values was 60 per cent while there was no deterioration in pituitary function if normal pre-operatively. Luteinizing hormone values, both basally and following gonadotrophin-releasing hormone, rose to normal after operation; several instances of sellar remodelling were observed radiologically, and no instance of relapse was found radiologically, biochemically or clinically. Thirteen patients desiring fertility have been observed since implantation; so far nine have become pregnant, in three instances without any additional therapy; since four patients became pregnant twice, a total of 13 pregnancies have occurred. No case of tumour expansion was observed during pregnancy. 90Y implantation can be considered as a therapeutic procedure in young female patients requiring fertility which is competitive with surgical methods, and together with a short course of bromocriptine if needed, could prove to be the treatment of choice.