The N-nitrosomethylurea (NMU)-induced transplacental blastomogenesis in rats was studied under the effect of pre- and postnatal glucose administration. On the 21st day of pregnancy NMU (20 mg/kg) was intraperitoneally administered to rats. From the 7th day of pregnancy experimental rats were treated with 10% glucose solution instead of drinking water, and during 1.5 months after delivery they and their progeny were given 5% glucose solution. The foetal weight in glucose-treated pregnant rate increased. A significant increase of tumour frequency was detected in the progeny of these rats. In male progeny tumours of the nervous system and kidneys typical of NMU effect prevailed and in females--tumours of other organs and tissues, particularly of the mammary gland, pituitary and hemopoietic system. Possible mechanisms of the modifying effect of glucose on the transplacental blastomogenic action of NMU are discussed.