The optimal temperature for the growth ofAspergillus parasiticus and the formation of aflatoxins B1 and G1 on whole wheat bread (sliced and packed) was 25°C. The optimal “total acid content” (Sauregrad) was 5.0. Incubation in light caused no reduction in aflatoxin yields. The optimal temperature for the growth ofPenicillium expansum on whole wheat bread was 10°C and was between 20° and 25°C for the biosynthesis of patulin. Patulin formation was not influenced by the “total acid content” but was greater under the influence of light than darkness. With increase of incubation time the yields of patulin decreased, probably due to an inactivation by SH-compounds.