Antipyrine kinetics were determined in 6 healthy volunteers before and after the end of a 1 week treatment period of ranitidine 150 mg twice a day. The mean antipyrine half-life (h) was before 12.6 +/- 4.6 h and after ranitidine treatment 12.0 +/- 2.6 h. Antipyrine clearance (ml/min) and volume of distribution (1) were not altered following ranitidine administration. The results suggest that ranitidine has no influence on antipyrine-metabolism in healthy volunteers.