Mycotoxins zearalenone and vomitoxin (4-deoxynivalenol) are often joint contaminants of grains infested by micromycetes of the genus Fusarium. Toxic effects of both mycotoxins on experimental organisms and farm animals are well known, but we have not found any literary reference to toxic effects of the combination zearalenone and vomitoxin. Embryotoxic effects of zearalenone, vomitoxin and combinations of various doses of zearalenone with constant addition of vomitoxin were studied in a three-day chick embryo. The objective of the study was to determine the coaction of vomitoxin on zearalenone embryotoxicity. Thermostat-incubated fertile eggs of White Leghorn hens were candled after three-day incubation, the shell above the embryo was removed, and within the embryotoxicity range zearalenone, vomitoxin and various doses of zearalenone with constant addition of 2 micrograms vomitoxin were applied to morphologically normal embryos. The groups of ten embryos were applied mycotoxins and their combinations in 10 microliters of their solutions to amnions using a special glass micropipette. Control group comprised twenty embryos which were applied 10 microliters of solvents used, 1% NaHCO3 and 10% ethanol. The eggs were covered with glass plates and their incubation was going on until the eighth day of their development. The embryos that died during incubation were discarded. On the eighth day of development, surviving embryos were taken out from the eggs and malformations of head, orofacial region, body wall, limbs and heart were determined microscopically. Tab. I shows total numbers of dead and malformed embryos after application of the particular doses of zearalenone, vomitoxin, their combinations and control solvents. The embryotoxicity range started at a dose of 5 to 20 micrograms per embryo. Zearalanone did not have any teratogenic effects on chick embryos. Applications of high doses of zearalenone (100 and 30 micrograms) instantly caused arrhythmia, atrio-ventricular dissociation or even heart stoppage. The beginning of the embryotoxicity range for vomitoxin was found to be within the narrow range of 1 to 3 micrograms per embryo. Among malformations, only a defect of the interventricular septum of the heart was found in 4% of the cases. The combined embryotoxic effects of zearalenone and vomitoxin were of additive, and mostly embryolethal nature. Among the malformations searched for, only 5% of the embryos exhibited a defect of the interventricular septum of the heart. Due to the good prediction fitness of chick embryo that has been proved by estimates of mycotoxin toxicity to mammals it is possible to suppose that toxic effects of the frequently occurring combinations of zearalenone and vomitoxin in fusarium-infected feeds will also be of additive nature for farm animals.