Using 3H-mepyramine and 3H-tiotidine to label, respectively, the histamine H1- and H2-receptors, we have assessed the distribution of these receptors in five distinct areas of guinea-pig brain. With regard to the H2-receptor, we could detect no binding in either the cerebellum or pons-medulla, whereas the distribution in the other brain areas was corpus striatum greater than cortex greater than hippocampus. This was in contrast to the distribution of the H1-receptor which was found to be in all areas studied but predominantly in the cerebellum.