A controlled crossover study was carried out on five volunteers to substantiate reported effects of fat intake on the bioavailability of griseofulvin. The urinary excretion of 6-demethylgriseofulvin was monitored for 24 h following the administration of 125-mg griseofulvin tablets in the fasting state and after a fatty diet. Statistical analysis of excretion data indicated a significant increase in both rate and extent of absorption of griseofulvin as a result of fat intake. Excretion rate profiles obtained permitted insight into mechanisms possibly involved in the observed drug-diet interaction.