Two colour morphs, red and grey, are recognized in the death adder, Acanthophis antarcticus, an Australian elapid snake. The inheritance of these morphs appears to be controlled by two alleles at a single autosomal locus, with red dominant to grey. Both morphs show seasonal changes in dorsal reflectance. They show similar reflectance patterns in winter, whereas in summer red animals become less reflectant, grey animals become more reflectant. Populations in northern and eastern Australian contain predominantly red snakes, whereas southern populations consist of mostly grey snakes. Selection for crypsis through substrata colour matchng may be important in maintaining the polymorephism.