Treatment of bovine lateral saphenous vein (cranial branch) and dorsal metatarsal artery with lysergamide (lysergic acid amide), an alkaloid in abundance in tall fescue, resulted in vasoconstriction similar to that previously shown for the ergot alkaloids ergonovine and ergotamine. Preincubation of tissues with lysergamide resulted in partial inhibition of the contractile response induced by the selective adrenergic agents phenylephrine and BHT-920 (P < .05), indicating partial agonist or antagonist activity of lysergamide at these receptors. Bovine vessels were strongly contracted by serotonin, and the response was markedly inhibited (P < .01) when tissues were preincubated with lysergamide. Studies with selective serotonergic agents indicated that lysergamide may have predilection for serotonin-2 receptors (5-HT2). Thus, lysergamide by itself has vasoconstrictor activity and acts as a partial agonist or antagonist at adrenergic and serotonergic receptors. Further studies are needed to establish the exact receptor effects of lysergamide. However, it is evident that this important alkaloid found in tall fescue infested with the endophytic fungus Acremonium coenophialum should be given consideration in studies designed to alleviate the fescue toxicosis syndrome in cattle.