First, the pharmacokinetics of antipyrine were studied in 12 healthy male and female volunteers (i) before misoprostol, (ii) after they had received misoprostol 400 micrograms twice daily for 28 days and (iii) after a further 28 days during which no misoprostol was taken. The plasma half-life and area under the plasma concentration-time curve of antipyrine were unchanged. The findings suggest that misoprostol is not an hepatic enzyme inducer. Second, 12 healthy male and female volunteers took propranolol 80 mg twice daily for four weeks; during the second and third of these weeks the volunteers also took misoprostol 400 micrograms twice daily. The plasma concentrations of propranolol under these steady state dosing conditions increased when misoprostol was added to propranolol. The mechanism underlying this finding should be clarified.