The proteins of venom reservoirs from 25 hymenopteran species from 21 genera were investigated with regard to their protein composition and immunological similarities. It was found that low mol. wt proteins and polypeptides are typical for the venoms of ants, social wasps and bees. Six species of ichneumonoid parasitic wasps lack these low mol. wt proteins. Except for bee venoms none of the low mol. wt proteins contain mannose. The venoms of ichneumonoid parasites and ants contained primarily acidic proteins, whereas those of social wasps and bees contained abundant neutral and basic proteins. Immunological analysis showed that a number of venom proteins from parasitic braconid (Chelonus ) wasps shared conserved immunoreactive determinants with the venom proteins of higher Hymenoptera, including some not of parasitic habit. Implications of phylogenetic relationships among hymenopteran species are discussed.