The hepatocarcinogenicity of aflatoxin BI in rats, ducks and rainbow trout has been convincingly demonstrated (1). In contrast, adult mice appear to be resistant to the toxic and carcinogenic effects. Newborn and infant mice are more sensitive to the effects of different hepatocarcinogens (2,3) and also to AFB, which induced hepatomas in newborn C57BL/6 x C3H FI I mice (4). A singl dose model of aflatoxin hepatocarcinogenesis was tested in infant C57BL/6 mice. AFBI was administered i.p. on day 7 after birth and the following data were investigated: 1) Changes in the activities of microsomal cytochrome P-450 dependant enzymes and conjugating enzymes in the course of the 20-month-Iong aflatoxin hepa- tocarcinogenesis study. At intervals of 6,8,12,18 and 20 months a ter AFBI administration, the concentrations of cyt P-450 andb and the acti- 5 vities of NADPH-, NADH-cyt c reductase, AOH, ADM, EH and GST were deter- mined. 2) Effect of continually administered diethyldithiocarbamate on the course of aflatoxin carcinogenesis. MATERIALS AND METHODS Aflatoxin BI was prepared biosynthetically in our laboratory and was checked for purity chromatographically, spectrophotometrically and by NMR.