Patulin is a metabolite of numerous Aspergillus and Penicillium species. It is toxic to a wide range of biological systems including microorganisms, plants and animals. Patulin has also been shown to be carcinogenic to mice. The susceptibility of man to this toxin is unknown at this time. However, when the numerous biological systems affected by patulin are considered, it is likely that man would also be susceptible to the toxic effects of this compound in some manner. Thus, patulin must be considered a potential health hazard. The fact that patulin can be produced by a number of penicillia at refrigeration temperatures is a source of possible concern. Many of these molds are found on refrigerated food products and the possibility that patulin production could occur during refrigerated storage is very real. However, the reactivity of patulin with sulfhydryl groups and other food components may cause its apparent disappearance from a food product. Whether the compound breaks down and disappears or is simply chemically altered to a non-detectable form is not known. Apparently toxicity is lessened, though it is not known if low pH or reactions with digestive enzymes might reverse these reactions or liberate free patulin in the gut. Certain foods such as cheeses and cured meats which are low in carbohydrates and high in protein do not appear to support patulin production to any great extent. This combined with the reactivity of patulin with sulfhydryl groups seems to lessen the danger of patulin occurrence in these foods. However, apple products and grain based products may pose more of a potential problem. Apple products are of particular concern since common apple rotting molds are frequent producers of patulin and because of the stability of patulin in these products. Further work is necessary to determine more completely the foods most likely to be contaminated with patulin. Presently, foods high in carbohydrates would appear to be of greater concern than foods low in carbohydrates and high in protein. Refrigerated storage of foods will not necessarily guarantee that they will remain free of patulin since many molds capable of producing patulin can do so at low temperatures. Further work is also needed to determine the fate of patulin as it undergoes reactions with sulfhydryl groups and other food components to determine if there are conditions under which patulin can be regenerated or recovered in a toxic form.