The minimum inhibiting concentrations (MIC) of delta9-tetrahydrocannabinol (THC) and cannabidiol (CBD) for staphylococci and streptococci in broth are in the range of 1-5 mug/ml. In the same range, both compounds are also bactericidal. In media containing 4% serum or 5% blood the antibacterial activity is strongly reduced (MIC 50 mug/ml). Gram-negative bacteria are resistant to THC and CBD.