Zearalenone, an estrogenic toxin produced by several Fusarium sp., was detected by two chromatographic methods in grain and food samples from several farms of th Buenos Aires Province. Suspected zearalenone spots were identified by comparing their Rf against that of the pure substance, by their change of behaviour under ultraviolet light of different wavelengths, by comparing the Rf against a standard preparation after thin layer chromatography in four different solvent systems, and by color reactions obtained after spraying reagents on the thin layer chromatographic plates. Sixteen of 55 samples were positive, with concentrations of the toxin ranging from 200 ppb to 750 ppb. Only Fusarium graminearum was isolated from eleven of these samples, indicating that the fungus was inactivated by heat or antifungal treatments.