antisnake activity of extracts and essential oil of nectandra megapotamica was tested in vitro against the bothrops diporus venom (yarar'a chica). inhibitory activity of the hemolytic action on the aqueous extract and essential oil; inhibition of the procoagulant action on hexanic extract and condensed water from steam distillation; and inhibition of the proteolytic activity on alcoholic extract and condensed water was found. in all cases, the main antisnake venom activity was found on plant material collected in the autumn. the chemical composition of the n. megapotamica essential oil was characterized during different vegetative states finding a clear predominance of mono- (21.0-31.7) and sesquiterpene (58.5-68.9) hydrocarbons. the differences found with previous results published for this species, growing in other geographic places, opens the option for the existence of chemical types.