The snake venomic of Crotalus durissus terrificus was analyzed by 2-D and 1-D electrophoresis and subsequent MS/MS and enzymatic assays. The venomic of the South American rattlesnake comprises toxins from seven protein families: phospholipases A(2), serine proteinases, ecto-5'-nucleotidases, metalloproteinases, nerve growth factors, phosphodiesterases, and glutaminyl cyclase. The venom toxin composition correlates with the clinical manifestation of the crotalinae snake bites and explains pathological effects of the venom such as neurotoxicity, systemic myonecrosis, hemostatic disorders, myoglobinuria, and acute renal failure. The vast majority of toxins are potentially involved in neurotoxicity, myotoxicity, and coagulopathy. The predominant venom components are neurotoxic phospholipases A(2) and serine proteinases. The venom is a rich source of 5'-nucleotidases (7.8% of the identified toxins) inducing hemostatic disorders. Analysis of the venom protein composition provided a catalogue for secreted toxins. The venomic composition of Crotalus d. terrificus and venom gland transcriptome of the synonymous subspecies Crotalus d. collilineatus show differences in the occurrence of protein families and in the abundance of toxins. Some of the venom components identified by the proteomic analysis were not reported in the transcriptome of the Crotalus d. collilineatus venom gland. Enzymatic activities of the Crotalus d. terrificus venom were determined and correlated with the proteomic composition.