Hydraphiles are synthetic ion channels that function in synthetic liposomes. This report shows that they are cytotoxic to Gram-negative and Gram-positive bacteria, yeast, and mammalian cells. Their cellular toxicity compares favorably with that of other synthetic ionophores and rivals the potency of natural antibiotics. Whole cell patch clamping with mammalian cells confirms a channel mechanism in living cells suggesting that this family may comprise novel and flexible pharmacological agents.