The mycotoxin patulin is a common contaminant of fruit. Here, we demonstrate that patulin reduces the barrier properties of the intestinal cell line, caco-2 by specific effects on tight junction components. Within 5h of exposure to 100 microM toxin, the transepithelial electrical resistance of caco-2 monolayers was reduced by approximately 95% and the monolayer became more permeable to FITC-labelled dextrans of 4-40 kDa. Immunoblotting revealed occludin proteolysis and a significant reduction in ZO-1 levels. Patulin had no influence on claudin levels but marked changes in their distribution were observed. These data indicate that patulin decreases the barrier properties of caco-2 monolayers by modulation of the tight junction.