The Baja California Peninsula possesses a mosaic of ecoregions that offers a wide variety of environments for the species that here inhabit. Here we report biological variations in. Crotalus ruber lucasensis venom from arid, semiarid and tropical eco-regions. Lethal (1.4–6.8 mg/kg), edematogenic (0.3–0.5 μg) and defibrinogenating (from non-detectable to 20 μg) activities were found to have significant differences among eco-regions