Three new venom peptides were isolated from the Brazilian wasp; Protonectarina sylveirae and their complete amino acid sequences were determined by Edman degradation as well as by FAB-mass spectrometry. One (P-8) of them was a new analog of mastoparan family; therefore, we named it Protonectarina mastoparan. Another peptide (P-10) had an amino acid sequence homology with Ves-CP-T, a chemotactic peptide of wasp venom, and bombolitin-V, the venom peptide from bumblebee. The third peptide (P-6) was structurally unique, possessing an intramolecular disulfide bond. Not only Protonectarina mastoparan (P-8) but also P-6 and P-10 caused histamine release from rat peritoneal mast cells as potently as mastoparan (EC50s were about 1 x 10(-6) M for P-6 and 2 x 10(-6) M for P-10). In addition, P-10 in a concentration higher than 1 x 10(-5) M induced hemolysis though whose hemolytic activity was about a half potency of that of mastoparan. However, P-6 did not cause hemolysis up to the concentration of 10 microM. We have named them sylverin for the peptide P-6 and protonectin for the peptide P-10.