The essential oils of five different cultivars of Cannabis sativa contained as main compounds alpha -pinene, myrcene, trans-beta -ocimene, alpha -terpinolene. trans-caryophyllene and alpha -humulene. The content of alpha -terpinolene divided the cultivars in two distinct groups, an Eastern European group of cultivars of approximately 8% and a French group of cultivars of around 16%. Therefore, this compound might be suitable as a genetic marker for the two breeding centres for the fibre types of Cannabis sativa. The content of trans-caryophyllene was up to 19%. However, the content of caryophyllene oxide did not exceed 2%. The antimicrobial activity of the essential oil of Cannabis sativa can be regarded as modest. Nevertheless, cultivar differences were visible. Delta -9-tetrahydrocannabinol (THC) could not be detected in any of the essential oils and the amount of other cannabinoids was very poor. Copyright (C) 2001 John Wiley & Sons, Ltd.