The influence of prednisolone on the elimination of antipyrine has been investigated. The one-sample antipyrine clearance was estimated in 23 outpatients with obstructive lung disease before and after treatment with prednisolone 30 or 50 mg/day for 7 days. During prednisolone administration antipyrine clearance decreased from 54.9 +/- 14.8 to 51.7 +/- 14.6 ml/min (mean +/- SD; p less than 0.05). The results indicate that prednisolone decreases the rate of antipyrine elimination, but not to an extent suggesting a clinically important change in hepatic drug metabolism.