Four Border-Leicester X Merino wethers were used in a 4 X 4 Latin square experiment to study the effects of dietary sulphur on selenium absorption and retention. The basal diet contained 0.05% S and sodium sulphate was added to give additional treatment levels of 0.11, 0.17 and 0.24% total sulphur. Sodium selenate was added to all diets to bring the dietary selenium level to a constant 0.25 mg/kg. One hundred muCi 75Se as sodium selenate (specific activity 50 muCi/mg Se) was administered to the rumen per fistulam after a 10-day period of adjustment on each diet. Radioactivity in blood, urine, faeces and rumen digesta was measured at intervals over the succeeding 7 days. Twenty percent of the total activity in the rumen fluid was in the TCA supernatant fraction after 3 hours, and this proportion tended to increase slightly as sulphur intake increased. Fecal excretion of selenium accounted for between 44 and 51% of the dose after 7 days, the high levels being associated with increasing sulphur intake. However, these differences were not significant. Urinary excretion of selenium accounted for between 12% (0.05% S) and 22% (0.24% S) of the dose after 7 days, with treatment differences being significant. Levels of radioactivity in blood were significantly higher in sheep fed the 0.05% S diet compared with those fed the higher levels. The results show that sulphur affects apparent selenium excretion and suggest that the metabolism of these two elements is intimately related.