Viruses depend on cell metabolism for their own propagation. The need to foster an intimate relationship with the host has resulted in the development of various strategies designed to help virus escape from the defense mechanisms present in the host. Over millions of years, the unremitting battle between pathogens and their hosts has led to changes in evolution of the immune system. Snake venoms are biological resources that have antiviral activity, hence substances of significant pharmacological value. The biodiversity in Brazil with respect to snakes is one of the richest on the planet; nevertheless, studies on the antiviral activity of venom from Brazilian snakes are scarce. The antiviral properties of snake venom appear as new promising therapeutic alternative against the defense mechanisms developed by viruses. In the current study, scientific papers published in recent years on the antiviral activity of venom from various species of snakes were reviewed. The objective of this review is to discuss the mechanisms of resistance developed by viruses and the components of snake venoms that present antiviral activity, particularly, enzymes, amino acids, peptides and proteins.Key words: snake venom, viruses, antiviral agents. Review ARticle The Journal of Venomous Animals and Toxins including Tropical Diseases ISSN 1678-9199 | 2011 | volume 17 | issue 4 | pages 387-393 INTRODUCTIONViruses are obligate intracellular parasites that depend on cell metabolism for their own propagation. This intimate virus-cell relationship led viruses to develop numerous survival strategies aimed at protecting themselves from the host defense system (1-4).One of the criteria for a successful viral infection is the ability to remain inside the host cell for the time required to allow replication of the viral genomic nucleic acid, envelopment and the production of new infectious virus progeny. The first barrier to be overcome is the host innate immune response (5).The association between virus persistence and disease in the host may lead to a long term relationship that does not result in any chronic virus-induced symptoms or in a fatal disease (6). Persistent viral infections constitute an example of immune evasion and, consequently, a successful relationship (7). Antiviral therapy has changed the natural history of numerous viral infections, delaying progression of the disease, improving the quality of life of infected individuals and reducing the frequency of hospitalization (8-10). Nevertheless, one of the principal problems today is therapeutic failure, including antiviral drug resistance (11, 12).The rich biodiversity in Brazil is an important source of wealth, since the country is home to at least 14% of the world's species, giving it an enormous advantage over other countries with poorer biodiversity, principally in a century in which biotechnology is expected to play such an important role in the global economy (13). Snake venoms are composed of a mixture of proteins and peptides (90-95%), but also include free amin...