A RECENT communication by Vane et al. entitled “Tryptamine Receptors in the Central Nervous System”1 concluded, on the basis of indirect evidence, that the receptors for tryptamine and for serotonin (5-hydroxytryptamine) were the same. Because the authors neglected to mention some earlier evidence of a more direct kind which showed clearly that certain receptors for these two substances were different, we wish to direct attention to this contrary evidence before the conclusion about their identity becomes widespread.