Somatosensory and visual evoked potentials in the classical afferent primary pathways in cats anesthetized with alpha-chloralose were studied in order to characterize the effects of delta 9-tetrahydrocannabinol (THC) and the synthetic analog, dimethylheptylpyran (DMHP) on central sensory processing. THC and DMHP slowed primary cortical responses to radial nerve or ventralis posterolateralis (VPL) stimulation in a dose dependent manner. THC did not alter VPL activity evoked by radial nerve stimulation. Amplitude of the primary somatic response was depressed at the 4 mg/kg dose. Responses of visual cortex and lateral geniculate nucleus, evoked by stimulation of optic chiasm, were unchanged at the doses studied. However, the nonmodality-specific response of the anterior marginal association cortex to stimulation of either modality was depressed by THC. Data suggest the association cortex which exhibits sensory convergence was most sensitive to the effects of THC. Findings were consistent with a thalamocortical site of action for THC. DMHP produced similar effects and was more potent.