Seasonal abundance of some snake species from the Atlantic forest in southeastern Brazil was inferred from collection data gathered throughout twelve years at the Instituto Butantan in São Paulo, Brazil. The number of collected individuals of Chironius spp., Liophis miliaris, Spilotes pullatus, Tropidodryas spp., Micrurus corallinus, and Bothrops jararaca was significantly higher during the rainy season, whereas the number of Sibynomorphus neuwiedi was higher during the dry season. Erythrolamprus aesculapii, Xenodon neuwiedii, Tomodon dorsatus and Bothrops jararacussu did not show significant differences in the number of individuals collected at each of these seasons. Seasonality in captures may result from seasonal activity patterns. Food availability, tolerance to climatic conditions, reproductive cycle, and phylogenetic constraints are considered the main factors responsible for the observed patterns. A multivariate approach is recommended for analysis of annual activity.