A simple and economical method has been developed for the determination of patulin in apple juice. The sample is extracted with ethyl acetate in a diphasic dialysis system, and the extract is cleaned up by elution from a Sep-Pak cartridge. Patulin is detected and determined by reversed-phase high-performance liquid chromatography using a Novapak C18 column and an ultraviolet detector. The lower detection limit is 1 microgram l-1 and the recovery is 85% at the 20 micrograms l-1 level.