1. Using everted sacs of sheep ileum, selenate uptake was shown to be more rapid than selenite uptake. 2. Sulphate, thiosulphate and ouabain all inhibited the uptake of selenate. A Na+K(+)-ATPase is probably responsible for energizing the ileal brush-border transport of selenate. 3. The isolated, vascularly perfused ileum was shown to absorb selenate more rapidly than selenite. 4. The perfusion system described would appear to be a useful tool for studying the kinetics of intestinal absorption and the measurement of metabolic transformations within the mucosa.