The α-adrenergic receptor-blocking activity of six phenethylamine congeners was studied on the isolated rabbit ileum and uterus. The results obtained indicated that α-receptor blockade varied with the size and number of substituent groups on the terminal nitrogen and the α-carbon atom of the side chain. Activity is lost by disubstitution on the α-carbon atom or shifting the methoxy group from the ortho - to the para -position in the phenyl ring. One compound, U-0277, had a direct musculotropic action on the uterus. None of the compounds was as potent as phentolamine.