Three series of derivatives of N,N-dimcthyltryptamine, ~r tryptamine and gramine bearing substituents of varying electronic nature on the C-5 position were tested for acute toxicity, effect on barbiturate sleeping time, antireserpine effect, swim maze, variable interval conditioned behavior, and inhibition of monoamine oxidase. No correlation could be made between the electronic effects and their pharmacological activities. It was thus suggested that there exist different pharmacological receptors for the tryptamines and gramines. Key-Words: 5-Substituted N,N-Dimethyltryptamines, zc-Methyltryptamine, and Gramines -- Monoamine Oxidase Inhibitors -- Psychopharmacology.