Δ9-Tetrahydrocannabinol (THC) treatment inhibits the metastases of lung tumors in SCID mice. A549 cells (1 × 106) were injected intravenously into immunodeficient SCID mice. Experimental mice were given THC (5 mg/kg body weight) daily for 28 days starting 24 h after injection of the cells. At the end of the experiment, the animals were killed and lungs were harvested and weighed before evaluation of the metastatic lesions. (a) An illustration of metastatic lesions in murine lungs from different experimental groups. THC-treated mice showed both significantly reduced lung weight (b) and less metastatic lesions (c) in comparison to the vehicle-treated animals (n=6 for each experimental group) (**††P<0.001; compared to vehicle-treated and normal animals, respectively).