SK&F 93319 (icotidine), 2-[4-(3-methoxypyrid-2-yl)butylamino]-5-[(6-methylpyrid-3-yl )-methyl]- pyrimidin-4-one trihydrochloride, has been identified as a novel agent which combines into one molecule the ability to antagonize the actions of histamine at H1 and H2 receptors across a similar concentration or dose range. The degree of antagonism of vascular responses to histamine exceeds that possible with either an H1- or H2-receptor histamine antagonist alone. SK&F 93319 may have therapeutic utility in conditions requiring simultaneous antagonism of histamine at H1 and H2 receptors.