Three cases of renal dysfunction at birth were observed in premature babies exposed in utero to prostaglandin synthetase inhibitors (PSI) and corticosteroids. Transient water and sodium retention with uraemia occurred in one patient, and severe acute renal failure with marked hyperkalaemia in twins. These findings may be due to impairment of prostaglandin (PG)-mediated renal adaptation to stress conditions after transplacental passage of PSI. Corticosteroids may also have affected PG synthesis inhibition.