Over the past ten years it has become quite apparent that mycotoxins, or toxins produced by fungi, are responsible for a wide variety of human and animal illnesses and, in many cases, deaths. Consequently, the study of the metabolites produced by fungi and the possible occurrence of such metabolites in foodstuffs is of critical importance. It is the purpose of this paper to outline the approach taken at the U.S. Food and Drug Administration in evaluating the possible hazard to human health posed by the growth of molds on foods, and to elaborate upon the results of studies sponsored by FDA relative to the metabolites produced by four mold species frequently found on foodstuffs. i.e., S. atra, P. islandicum, P. viridicatum and A. versicolor.