The strongly surface-active polypeptide antibiotic alamethicin (m.w. ~ 1700) interacts with artificial black lipid membranes to form voltage gateable ionic channels with five discrete conductance states. The channels fluctuate between these states with transition rates which depend little on the applied voltage. Within any conductance state, the behavior is approximately ohmic and similar to bulk solutions. When added on one side only, alamethicin confers upon a phosphatidyl-ethanolamine-decane black film a pronounced asymmetry. The alamethicin channels are only slightly ion selective, their rate of formation is strongly dependent on the alamethicin concentration, on the voltage across the membrane and on the ionic strengths.