The interrelationship in metabolism between dietary selenium (Se) and copper (Cu) was investigated in sheep receiving a diet with or without sodium bicarbonate (NaHCO3). A sheep finishing diet, containing 0·3 mg Se/kg DM and 7·4 mg Cu/kg DM, and supplemented with 1·0 mg Se (as Na2SeO3) and/or 15·0 mg Cu (as CuSO4) and/or 40 g NaHCO3 per kg feed, was fed to young ewes for a period of 64 days. Hepatic Cu concentration and net accumulation were not affected by NaHCO3 supplementation. Furthermore, no evidence was found in blood, tissues or faeces to show that NaHCO3 influenced Se metabolism. However, hepatic Cu concentration was raised from 354 to 422 mg/kg DM (P<0·05) when the diet was supplemented with 1 mg Se/kg DM, independent of the level of dietary Cu. Furthermore, hepatic Cu retention was significantly (P<0·05) influenced by a Se × Cu interaction, namely when the diet was supplemented with 15·0 mg CuSO4 or 1·0 mg Na2SeO3 /kg DM or both, 0·084, 0·081 and 0·088 of the dietary Cu respectively was retained in the liver, compared to 0·047 in the sheep on the basal diet. In addition, supplementation with Se and Cu together increased hepatic Se concentration to a greater extent (P<0·001) than when Se alone was added to the feed (3·65 v. 5·17 mg Se/kg DM respectively). The concentration of Se in both muscle tissue and in rumen bacteria was raised (P<0·001) by Se supplementation, but more so (P<0·05) in both cases when Cu was not added to the diet. Interactions between Se and Cu were not influenced by NaHCO3 supplementation in the conditions of this study.