1. Early changes (0-44 hr) in liver and plasma lipid levels and in the rate of hepatic lipogenesis were measured in male chicks after a single intramuscular injection of oestradiol-17 beta. 2. Chick liver slices were employed to measure the rate of lipogenesis de novo using 3H2O and the rate of triacylglycerol synthesis from [9, 10-3H] palmitate at various times after injection. 3. The results suggest that oestrogen-induced lipogenesis occurs initially by a rapid and coordinated stimulation of the total hepatic capacity for lipogenesis de novo and for triacyglycerol synthesis from fatty acids. 4. The results are discussed in relation to oestrogen-induced changes in hepatic lipogenic enzymes.