The effects were assessed of delta'THC (the psychoactive component of cannabis) and CBD and DMHP-CBD (the non-psychomimetic components of marijuana derivatives) on 14C labelled serotonin release from normal platelets, when incubated with patient's plasma obtained during migraine attack. A statistically significant inhibitory effect (p greater than 0.005) of 14C serotonin release was found at 10(-5)M, 10(-6)M, 10(-7)M delta'THC concentrations. Plasma of migraine patients obtained in attack-free periods revealed no significant inhibitory effect on 14C serotonin release from normal platelets using the same delta'THC concentration. CBD and DMHP-CBD had no significant inhibitory effect on 14C serotonin release from normal platelets when tested either at migraine-free period plasma or plasma obtained during migraine attack.