Estradiol implants in chicks resulted in marked elevation of all major plasma lipids with greatest increase in triglyceride (TG) followed by phospholipid (PL) and cholesterol (C). During the two-wk period, plasma TG level in estrogen (E)-treated chicks increased to about 45 times that of controls (139.6 vs 6,368.3 mg/dl). The level of cholesterol also increased steadily during the same period, attaining nearly a six-fold increase in comparison with the control (150.7 vs 871.8 mg/dl), and the level of PL was markedly elevated from 209 to 2,861 mg/dl. Besides the induction of hyperlipidemia, E treatment also resulted in a notable alteration in the fatty acid composition of plasma lipids; there was an increase in oleic acid concomitant with a decrease in polyunsaturated fatty acids, particularly, linoleic acid. One day after implantation, the percentage of oleic acid in TG fraction increased from 39.2 to 43.7%, reaching 55.4% of the total fatty acids at day 14. In contrast, the levels of linoleic and arachidonic acid decreased significantly from 16.1 to 8.3% and 4.3 to 0.6%, respectively, during the same period. In cholesteryl ester (CE) and PL, the oleic acid level also increased from 25.2 to 47.3% in the former and from 11.9 to 29.6% in the latter, reflecting enhanced hepatic lipogenesis. Analysis of plasma lipoproteins in E-treated chicks revealed dramatic alterations in the concentrations of lipids and protein in individual lipoprotein fractions, especially very low density lipoprotein (VLDL) fraction.(ABSTRACT TRUNCATED AT 250 WORDS)