The authors describe a thin-layer chromatographic method for determining patulin in fruit and vegetable products which is suited for routine work in hygiene practice. The samples are extracted with ethyl acetate, and the extracts are purified on a Florisil column. Separation is performed by means of a one-dimensional technique, using toluene/ehtyl acetate/formic acid (5 + 4 + 1), or, in the presence of interfering contaminants, by means of a two-dimensional technique, using benzene/methanol/glacial acetic acid (90 + 5 + 5) for the first run, and toluene/ethyl acetate/formic acid (5 + 4 + 1) for the second run. Patulin is detected by spraying with a benzidine solution, after chlorination. The limits of detection are 5 microgram/l of juice and 5 microgram/kg of fruit or vegetable. Derivatization with acetic anhydride/pyridine is used for corroborating the results obtained. The significance of 5-hydroxymethylfurfural as an interfering substance in apple juices is discussed.