The effect of pregnancy has been studied in 10 mothers with Wilson's disease. Three were presymptomatic but had the typical biochemical lesion, two of these were receiving penicillamine treatment at the time of conception, the third had yet to be diagnosed. The remaining seven mothers had had symptoms of Wilson's disease and had been receiving treatment for periods ranging from two and a half to 19 years. These mothers had 15 pregnancies between them, 13 went to full term but two ended prematurely at 26 and 30 weeks. In only one did pregnancy have an unfavourable effect on the Wilson's disease; this mother had been on penicillamine for only two and a half years in a suboptimal dose because of drug induced thrombocytopoenia. In addition she had extensive oesophageal varices and pregnancy was complicated by toxaemia. The other nine patients remained well and two had three pregnancies each. On six occasions penicillamine was taken throughout pregnancy, but in seven it was discontinued from the sixth to the twelfth week. All 15 babies were normal but one died of extreme prematurity (26 weeks gestation). Pregnancy does not appear to be contraindicated in well treated Wilson's disease and penicillamine does not seem to pose an undue risk to the foetus.