To evaluate the potential interaction of propylene glycol on hepatic drug oxidation, antipyrine disposition was measured in 10 healthy subjects who received 1.2 gm antipyrine alone on one occasion and 1.2 gm antipyrine with propylene glycol on a second occasion. Propylene glycol was given as a 5 ml dose every 4 hours during the 48 hours of the study. Propylene glycol had no effect on antipyrine half life (11.7 hours control vs. 12.1 hours treatment), clearance (42.6 vs. 39.2 ml/min), or volume of distribution (42.1 vs 41.9 L). At a dose similar to that used as a vehicle for administration of other drugs, propylene glycol had no significant effect on antipyrine clearance in humans.