Two N-isopropylnorephedrines and their four possible decalol analogs were compared pharmacologically. Four of the six compounds at a concentration of 1 x 10(-4) M caused a potentiation of D(-)-norepinephrine (NE) contraction of the rat vas deferens and increased the maximal response of the preparation to NE. Pretreatment in vivo with reserpine (5 mg/kg ip) 24 hr before the experiment in vitro did not change these effects. At a concentration higher than 1 x 10(-3) M all of the decalin analogs antagonized the effects of NE. All of the analogs lowered the dog blood pressure briefly. The lowering of blood pressure was augmented by alpha-adrenergic blockade and was not changed by beta-adrenergic blockade, atropine, or a ganglionic blocking agent. Tachyphylaxis was not observed. The spontaneous contraction of isolated rabbit atria was depressed by the substances at concentrations of 1 x 10(-4)-1 x 10(-3) M. Catecholamine uptake in rat vas deferens was lowered by the substances and all of them produced a release of catecholamines from vas deferens. By virtue of the conformational rigidity of the decalols, possible inferences concerning the stereochemical aspects of the interaction of the ephedrine analogs with adrenergic neurone-receptor sites are discussed.