Observations are reported on 41 pregnancies in 27 patients who initially had infertility and raised serum prolactin concentrations. Associated symptoms were secondary amenorrhoea (81 per cent) and galactorrhoea (81 per cent). All patients were at risk of pituitary expansion during pregnancy, especially these 19 (70 per cent) with radiological evidence of pituitary tumours. Fifteen patients had 21 pregnancies after pituitary implantation with 90yttrium; 14 patients had 20 pregnancies without prior pituitary implantation or any other attempt to prevent tumour expansion. During pregnancies, tumour enlargement as shown by diminished visual acuity, visual field defects, severe headaches, diabetes insipidus and radiological changes occurred only in 3 of the 14 patients who had not had implants. Two patients who became pregnant both before and after pituitary implantation suffered tumour expansion in their pregnancies before implantation, but not when pregnant after the operation. The induction and Cesarean section rates were about 30 per cent in 32 term pregnancies in 25 patients. Details of how pregnancy was achieved and the associated obstetric problems are given.