1. The influence of nutrition and chronic lead (Pb) administration on the level of eicosanoids and their precursors was evaluated in serum and liver from chicks fed defined diets. 2. Dietary Pb consistently increased arachidonic acid, the arachidonate/linoleate ratio, and hepatic non-protein sulfhydryl concentration. 3. Hepatic microsomal fatty acid elongation activity was decreased by Pb. 4. Cottonseed oil, calcium and methionine interacted with Pb, affecting liver and serum fatty acid profiles. 5. Tissue levels of leukotriene C4 rose significantly with Pb or correlated with Pb-compromised body weight in only one experiment. Serum prostaglandins E2 and F2 alpha were unchanged by treatments. 6. The results suggest that an increase in precursors is not consistently reflected by tissue levels of eicosanoids.