The effect of dietary fat on the availability of selenium was investigated in chicks fed either 4 or 20% butter, olive oil, rape oil, corn oil or sunflower oil in the diet for 3 weeks after hatching. Plasma glutathione peroxidase (GSH-Px) activity was used as an indicator of the body selenium status. In addition, the intestinal absorption of sodium selenite (75Se-labeled) was determined by using both the in vivo ligated loop procedure and oral administration of the isotope. The plasma GSH-Px levels increased with increasing proportion of the polyunsaturated fatty acids in the diet. Increasing the amount of fat from 4 to 20% significantly enhanced the GSH-Px activity in the groups receiving butter or olive oil, but had no effect in animals fed the unsaturated fats. The absorption of [75Se]selenite from the ligated duodenal loops tended to be reduced in chicks fed corn oil or sunflower oil as compared to the animals receiving butter in their diet. On the other hand, the type of dietary fat did not appear to affect the absorption of the orally administered selenite. The present study demonstrates that the type of dietary fat can affect the plasma GSH-Px levels in chicks without altering the intestinal absorption of selenite. However, the results on the absorption of the intraduodenally injected sodium selenite suggest that dietary fat plays some role in the intestinal transport of selenium.