ABSTRACTWhile it has previously been suspected that Byssochlamys spp. may grow in canned fruits and produce the mycotoxin patulin, direct evidence for this occurrence is not available: The effects of different initial static oxygen levels, and temperatures on the formation of patulin by B. nivea in Concord grape juice packed in glass jars was examined. The greatest amount of patulin(0.31 mg/SO ml) was formed after 28 days in jars with a 5.1 cm headspace incubated at 20°C. Patulin was formed more rapidly at 25° and 30°C, but declined in a mounts after reaching maximum values. Cultures of B. fulva and B. nivea produced less patulin in grape juice packed in glass jars with headspaces of 2.5 and 1.3 cm than in glass jars with a 5.1 cm headspace. More favorable conditions were used in this study to produce patulin than would be found in the commercial production of Concord grape juice.