Embryotoxicity: Aflatoxin B1 (AFB1), G1 (AFG1), and Patulin (PA) were investigated in NMRI mice for embryotoxic and teratogenic activity. These three mycotoxins were injected intraperitoneally or given orally on day 12 and 13 of pregnancy. AFB1 (15, 45, and 90 mg/kg ip or 45 mg/kg po) produced moderate retardation in fetal development and a dose-related increase of cleft palates, wavy ribs, and diaphragm changes. The effects after injection of AFG1 (45 to 90 mg/kg ip) were reduction of fetal weights, increase of diaphragm changes, and malformations of kidneys. PA (1, 25, 2, 5, and 3.75 mg/kg ip or 3.75 mg/kg po) was found to elevate the rate of cleft palates after 3.75 mg/kg. Dominant lethal assay: Neither PA (2, 5, and 5 mg/kg ip) nor AFB1 (15 and 45 mg/kg ip) increased the frequency of the dominant lethal mutations. Both mycotoxins showed no mutagenic activity in this test system. Cytogenetic studies: The capability of the three mycotoxins AFB1, AFG1, and PA to induce chromosome damages in vivo has been tested in the Chinese hamster by examination of bone marrow cells. The substances were tested in each of two oral doses (AFB1: 12, 5, and 25 mg/kg; 25 and 50 mg/kg; PA: 10 and 20 mg/kg). The present data show that the three mycotoxins induce chromosome aberrations in the following order of activity: PA greater than AFB1 greater than AFG1.