delta 9-Tetrahydrocannabinol (delta 9-THC) caused no change in either pilocarpine or acetylcholine (ACh)-stimulated salivary flow of the cat but significantly decreased salivary flow from the submaxillary gland of the car and dog during electrical stimulation of the chorda tympani. In contributing to this effect, delta 9-THC significantly decreased (47%) basal arterial blood flow to the submaxillary gland of the dog and markedly reduced (51%) the stimulated blood flow to the gland produced by electrical stimulation of the chorda tympani. The decrease in stimulated blood flow by delta 9-THC suggested an effect on the ACh of the gland. No decrease in the synthesis of ACh could be demonstrated in the submaxillary gland of the dog. A significant decrease (37%) in the release of ACh from transmurally stimulated guinea-pig ileum, a model tissue, was produced by delta 9-THC. These data suggest that delta 9-THC decreases electrically stimulated salivary flow by a mechanism involving the decrease in release of ACh which results in a reduction of blood flow to the submaxillary gland, and, also, less ACh for stimulation of the secretory cells of the gland.