The research literature can be confusing because of the vast number of nonproprietary names used by various authors for a specific drug. An attempt is made here to clarify the ambiguity regarding the stereoisomer, (-) erythro-alpha-methylnorepinephrine. This agent is used in dentistry as a vasoconstrictor (Neo-Cobefrin) and although its pharmacologic activilty is weaker than that of (-) norepinephrine, it appears that this agent can have significant pharmacologic effects at higher doses. Effects reported have consisted of decreased or increased blood pressure because of the activation of beta receptors or alpha receptors, respectively.