Diet composition may influence the activity of the HPA and HPT axes, which, in turn, modulates immune system function. The aim of the present study was to investigate the response of rat hormonal and immune parameters to feeding with a standard diet supplemented with cholesterol and vitamin E. The experiment was performed on Wistar rats fed for 6 weeks on a diet without supplementation, or the same diet enriched with cholesterol and/or vitamin E. Vitamin E supplementation caused a decrease in body weight gain and an increase in thyroid peroxidase activity as well as raised plasma concentrations of thyroid hormones and corticosterone. Supplementation with both cholesterol and vitamin E attenuated these effects. The cholesterol-enriched diet decreased plasma levels of ACTH while it stimulated the activity of 11β-hydroxylase deoxycorticosterone in the adrenals. Splenocyte proliferation in vitro was modified by the cholesterol-enriched diet but additional supplementation with vitamin E reversed these effects.