Atomic force microscopy was used to study the morphology of crude venom from the South American rattlesnake crotalus durissus terrificus. The results indicate that the crystallized crude venom has a high surface roughness with pores of diameters around 100 nm. Coiled filamentary structures of diameters of about 200 nm and lengths greater than 1000 urn, and large concave structures of diameter around 1000 nm, have also been observed dispersed over the main solid surface of the venom. Such structures may be related to aggregates of toxic enzymes or to bacteria or both. The coiled filamentary structures appear to be entangled on the pores of the venom surface in contrast to the large concave structures, which appear not to be bonded to the principal crystallized surface.