The uptake of added Se from selenite and selenate by barley and red clover was investigated in a pot experiment. Much more of selenate than of selenite was taken up but the Se concentrations in the plants declined more with time when selenate was the source. Increasing sulphate addition to the soil decreased the uptake of Se from selenate greatly and from selenite to a lesser extent. The ratio Se in the roots/Se in the tops shows that Se is more readily translocated from the roots when taken up from added selenate than from selenite. On the basis of these and other investigations it is concluded that selenite is a better source than selenate when the Se concentration in the plants has to be raised to a level sufficient for livestock nutrition.