Fluorometric TLC procedures are described for the determination of griseofulvin in human plasma and 6-demethylgriseofulvin in human urine. Griseofulvin is extracted from plasma with ether, and its metabolite, 6-demethylgriseofulvin, is extracted from urine with benzene. Both compounds are subjected to TLC on silica gel plates. The plates are scanned using the fluorescent mode of a spectrodensitometer. For griseofulvin, the quantitation limit is 20 ng/ml of plasma and the recovery is 100%; for 6-demethylgriseofulvin, the limit is 1 μ/ml of urine and the recovery is 96%. The methods were used to determine the plasma levels of griseofulvin and the amount of 6-demethylgriseofulvin excreted in the urine of human volunteers after a single oral dose of griseofulvin.