Short-term effects of small doses of aflatoxin (0.05 mg/kg of body weight twice a week) were studied in rhesus monkeys fed low-protein and high-protein diets. Animals on high- and low-protein diets without aflatoxin administration served as controls. There was no difference in weight gain, hemogram, serum protein levels, and liver function test results between aflatoxin-treated and control animals. However, morphological alterations in hepatocytes in the form of mild degenerative changes, focal areas of necrosis, and increased regenerative activity were seen in the aflatoxin-treated monkeys. Data on cell cycle analysis done by DNA content estimation through microfluorimetry on DNA-fluorescent, acriflavin-stained liver imprints revealed larger number of cells in the S and Gi2 phases in animals given aflatoxin. However, the changes in cell cycle, as well as in morphology, were more marked in the aflatoxin-treated, low-protein-diet group.