Molds were isolated from natural and processed Cheddar cheese previously treated with potassium sorbate. When potato dextrose agar fortified with up to 8,400ppm potassium sorbate and adjusted to pH 5.3 to 5.5, served as the substrate, Penicillium roqueforti, a mutant of P. roqueforti, Penicillium notatum, Penicillium frequentans, and Penicillium cyaneo-fulvum (all recovered from cheese), were able to grow in the presence of up to 5,400, 7,100, 2,300, 2,800, and 1,800ppm potassium sorbate, respectively.All of the penicillia studied depleted sorbate from liquid culture media; highest concentrations were degraded by P. roqueforti and its mutant. Depletion of sorbate from the medium was enhanced by a highly nutritious substrate and retarded by a minimal growth medium. Degradation of sorbate was accompanied by formation of a volatile compound with a hydrocarbon-like odor. This substance was identified as 1,3-pentadiene by means of gas chromatographic and infrared analyses. It is believed that the molds degrade sorbate into an inactive material through decarboxylation.