—The present paper reports the result of studies undertaken to determine the effects of the in vivo administration of Δ9‐THC on the ganglioside and sialoglycoprotein contents of rat brain subcellular fractions. Results indicate that the administration of the drug under both acute and chronic conditions brings about characteristic changes in the sialoglycoproteins and ganglioside content in all the subcellular fractions. Both sialoglycoproteins and ganglioside contents were markedly increased in microsomal and synaptosomal fractions and decreased in the mitochondrial fractions although the increase in the synaptosomal fractions has been found to be most striking. After chronic treatment, both ganglioside and sialoglycoprotein content did not change substantially in all the fractions except for a small increase in case of synaptosomal fractions. Copyright © 1976, Wiley Blackwell. All rights reserved