A sample of hashish was extracted consecutively with petroleum ether, benzene, and methanol. When tested intravenously in monkeys only the petroleum-ether fraction was active. This material was further fractionated. The only active compound isolated was Δ1-tetrahydrocannabinol. Cannabinol, cannabidiol, cannabichromene, cannabigerol, and cannabicyclol when administered together with Δ1-tetrahydrocannabinol do not cause a change in the activity of the latter, under the experimental conditions used. These results provide evidence that, except for Δ1- tetrahydrocannabinol, no other major, psychotomimetically active compounds are present in hashish.