Sperm morphology was studied in hybrid mice of genotype (C57BL X C3H)F1 following treatment with specific cannabinoids. Mice were treated for 5 consecutive days with the specific cannabinoid; 35 days after the last treatment, epididymal sperm were scored in the light microscope and assessed in the scanning electron microscope. The animals treated with delta9-tetrahydrocannabinol (delta9-THC) and cannabinol (CBN) had a statistically higher incidence of abnormal sperm than the controls. The incidence of abnormal sperm in the animals treated with cannabidiol (CBD) was not statistically different from the control value. The relative toxicity of the cannabinoids in these studies was delta9-THC greater than CBN greater than CBD. Normal sperm have a smooth kidney-shaped head with a prominent hook; abnormal sperm have shapes which include heads without hooks, banana-shaped heads, amorphous heads and folded heads.