The effects of water activity (aw) and temperature on growth of and ochratoxin A (OA) production by strains of Aspergillus ochraceus, Penicillium cyclopium, and Penicillium viridicatum were investigated. On agar media in which the aw had been adjusted by addition of sucrose or glycerol, the minimum aw values for OA production by A. ochraceus, P. cyclopium and P. viridicatum lay between 0.83–0.87, 0.87–0.90, and 0.83–0.86, respectively. At 24 C, optimum aw values for OA production by A. ochraceus and P. cyclopium were 0.99 and 0.95–0.99, respectively, whereas that of P. viridicatum varied and was 0.95 and 0.99 for the two strains tested. At optimum aw, the temperature range for OA production by A. ochraceus was 12–37 C, whereas that of P. cyclopium and P. viridicatum was 4–31 C. Optimum temperature for OA production by A. ochraceus was 31 C, whereas that of P. cyclopium and P. viridicatum was 24 C. On Edam cheese of 0.95 aw the minimum temperature for OA production by P. cyclopium was 20 C. On barley meal,...