Cyclopiazonic acid (CPA) is a toxic, indole tetramic acid that was originally isolated from Penicillium cyclopium Westling and subsequently reported to be produced by numerous species of Penicillium and Aspergillus. Among the species of Aspergillus that produce CPA is A. flavus, which is primarily known as a producer of the aflatoxins and is a frequent contaminant of corn, peanuts, and other commodities. The taxonomy of Penicillium species that produce CPA has undergone several revisions, but Pitt et al. concluded that the correct name for most saprophytic Penicillia that produce CPA is P. commune with P. palitans as a synonym. This would include the original isolate variously identified as P. cyclopium, P. griseofulvum, and P. verrucosum var. cyclopium. Pitt et al. also classified all molds used in the manufacture of white cheeses that produce CPA as P. camembertii. Based primarily on chemotaxonomical features coupled with conidial colors on Czapek yeast autolysate agar, Lund concluded that P. palitans was not just synonymous with P. commune, but was actually a distinct species. Despite some confusion with regard to the taxonomy of CPA-producing Penicillia, the fact remains that the various species of Penicillium and Aspergillus that produce CPA are ubiquitous and abundant in nature and are common contaminants of commodities that go into foods and feeds. Therefore, the potential for the contamination of commodities with CPA is widespread.