The efficacy of alpha and beta-D-glucose in causing insulin release and suppressing glucagon release from the isolated perfused rat pancreas was tested. In order to allow simultaneous assessment of glucose effect on both alpha and beta-cells, the pancreas was continually perfused with a physiological amino acid mixture (10 mM) which provokes glucagon secretion and also stimulates the beta-cells, provided glucose is present. Under these conditions the alpha-anomer of D-glucose at 3 and 6 mM proved significantly more potent than the beta-anomer in inducing insulin release and in inhibiting glucagon secretion. These data lend further support to the concept that alpha-cells and beta-cells contain glucoreceptors controlling glucagon and insulin seckretion and show that certain physiochemical properties of these receptors are alike in both types of cells.