Purothionin was isolated from wheat and its binding behavior to crude PC/CL (4:1) vesicles was studied. This protein was found to bind to the vesicles at pH 4,5 as well as at pH 7. Its was found that the vesicle became permeable to carboxyfluorescein and terbium, entrapped within the vesicles, only when the purothionin is added to the system. Since, no fusion of the vesicles was observed under the condition, it appears that the binding of the purothionin to the vesicles is followed by the channel formation in the bilayer through which carboxyfluorescein and terbium leak rapidly.