Macrophages and macrophage-like cells are important targets of HIV-1 infection at peripheral sites and in the central nervous system. After infection, these cells secrete a plethora of toxic factors, including the viral regulatory trans-activating protein (Tat). This protein is highly immunogenic and also serves as a potent chemoattractant for monocytes. In the present study, the exogenous cannabinoids delta-9-tetrahydrocannabinol (THC) and (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)phenyl]-trans-4-(3-hydroxypropyl) cyclohexanol (CP55940) were shown to significantly inhibit migration of human U937 macrophage-like cells to the Tat protein in a concentration-related manner. The CB(1) receptor-selective agonist N-(2-chloroethyl)-5Z,8Z,11Z,14Z-eicosatetraenamide (ACEA) had no effect on Tat-mediated migration. In contrast, the CB(2) receptor-selective agonist (1R,3R)-1-[4-(1,1-dimethylheptyl)-2,6-dimethoxyphenyl]-3-methylcyclohexanol (O-2137) exerted a concentration-related inhibition of U937 cell migration in response to Tat. Pharmacological blockage of CB(1) receptor signaling using the antagonist 5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-N-(1-piperidyl)pyrazole-3-carboxamide hydrochloride (SR141716A) had no effect on CP55940-mediated inhibition of macrophage migration to Tat, whereas treatment with the CB(2) receptor antagonist (1S-endo)-5-(4-chloro-3-methylphenyl)-1-((4-methylphenyl)methyl)-N-(1,3,3-trimethylbicyclo(2.2.1)hept-2-yl)-1H-pyrazole-3-carboxamide (SR144528) reversed the CP55940-mediated inhibition of migration. In addition, THC had no inhibitory effect on U937 migration to Tat after small interfering RNA knockdown of the CB(2) receptor. Collectively, the pharmacological and biochemical knockdown data indicate that cannabinoid-mediated modulation of macrophage migration to the HIV-1 Tat protein is linked to the CB(2) cannabinoid receptor. Furthermore, these results suggest that the CB(2) cannabinoid receptor has potential to serve as a therapeutic target for ablation of HIV-1-associated untoward inflammatory response.