The effects of the enantiomers of 11-hydroxy-delta 8-tetrahydrocannabinol-dimethylheptyl (11-OH-delta 8-THC-DMH) on spontaneous activity, rectal temperature, tail-flick latency, and catalepsy were studied in mice and in the dog static-ataxia model to determine the relative potency of each enantiomer. The (-)-enantiomer was active in all tests between 3-100 micrograms/kg, while the (+)-enantiomer was inactive at 30 mg/kg in the mouse and 1 mg/kg in the dog. The (-)-enantiomer was 100-800 times more potent than delta 9-THC in the mouse. The high degree of enantioselectivity and potency are suggestive of an interaction at a specific site such as a receptor.