Three novel peptides were isolated from the venom of the spider Heriaeus melloteei (Thomisidae) and characterized. The peptides named Hm-1, 2 and 3 blocked voltage-gated sodium channels at concentrations in the order of 100 nM. Activity of the purified peptides was investigated in sodium channel isoforms of mammals and insects. Hm-1 and 2 appeared to act as pore blockers, whereas Hm-3 modulated the channel activation process. The toxins described exhibit minor similarity with other known peptides and may therefore constitute new groups of sodium channel ligands.