Puroindoline-a (PIN-a) and α1-purothionin (α1-PTH), isolated from wheat endosperm of Triticum aestivum sp., have been suggested to play a role in plant defence mechanisms against phytopathogenic organisms. We investigated their ability to form pores when incorporated into giant liposomes using the patch-clamp technique. PIN-a formed cationic channels (≈ 15 pS) with the following selectivity K+ > Na+ >> Cl. Also, α1-PTH formed channels of ≈ 46 pS and 125 pS at +100 mV, the selectivity of which was Ca2+ > Na+ ≈ K+ >> Cl and Cl >> Na+, respectively. In isolated mouse neuromuscular preparations, α1-PTH induced muscle membrane depolarization, leading to blockade of synaptic transmission and directly elicited muscle twitches. Also, α1-PTH caused swelling of differentiated neuroblastoma NG108-15 cells, membrane bleb formation, and disorganization of F-actin. In contrast, similar concentrations of PIN-a had no detectable effects. The cytotoxic actions of α1-PTH on mammalian cells may be explained by its ability to induce cationic-selective channels.