Concentrations of purine bases in venoms are highly correlated with concentrations of their respective nucleosides, suggesting that their primary function is to support production of the nucleosides, the roles in envenomation of which have been well characterized. Ovophis okinavensis was excluded from plot 13a because no adenine was detected in that venom. Elapids, red; viperines, green; and crotalines, blue. Taxonomic abbreviations: Apl, Agkistrodon piscivorus leucostoma; Bmo, Bothrops moojeni; Bmu, Bungarus multicinctus; Cc, Cerastes cerastes; Cdt, Crotalus durissus terrificus; Cvv, Crotalus viridis viridis; Ds, Daboia siamensis; Dp, Dendroaspis polylepis; Mss, Micrurus spixii spixii; Ms1–3, Micrurus surinamensis 1–3; Nk, Naja kaouthia; Oh, Ophiophagus hannah; Oo, Ovophis okinavensis; Pe, Protobothrops elegans; Pf, Protobothrops flavoviridis.