AbstractThe effects were determined of dietary fat and selenium (Se) levels on prostaglandin (PG) production in rat blood, kidney, and colon mucosa. For 30 weeks, male Wistar‐derived MRC rats were prefed diets containing low (6 g/367 kcal) or high (20 g/367 kcal) levels of fat with one of three Se supplements from sodium selenite: 0.0, 0.1, or 2.0 ppm Se. PG production was stopped by adding aspirin immediately following removal of the blood, kidney, and colon samples. Separate samples were allowed to incubate 10 or 60 minutes before blockage of PG production for determination ofex vivoPG production. Prostaglandin E2(PGE2), thromboxane B2, and 6‐keto‐prostaglandin F1α(6‐keto‐PGF1α) were measured by radioimmunoassay following separation on silicic acid columns. Basal levels of the three PGs were not influenced by diet. PGE2production in the colon was highest in the group fed the high‐fat diet that contained 2.0 ppm Se at 10 and 60 minutes, but PGE2production in the blood and kidney were not altered by diet. Thromboxane B2production in the rats’blood was higher in those prefed high‐fat diets, but it was not influenced by dietary Se. Production of 6‐keto‐PGF1αin the blood and thromboxane B2and 6‐keto‐PGF1αproduction by the kidney and colonic mucosa were not influenced by either dietary fat or Se.