Tetranactin is a macrotetrolide and a monovalent cation ionophore that has been found in S. aureus and has antibacterial, insecticidal, and mitogenic activities. It exhibits an equilibrium permeability ratio 1,000-fold greater for lithium than sodium or cesium ions accross bilayer membranes at low voltages. Tetranactin inhibits the growth of Gram-positive bacteria and C. miyabeanus and R. solani fungi when used at concentrations less than 0.9 μg/ml. Tetranactin (0.5-1.5 μg per insect) dose-dependently increases the mortality of adult C. chinensis weevils up to 100% and has mitogenic activity against T. telarius when sprayed onto plants with an LC50 value of 9.2 μg/ml. It reduces IL-1β- and cAMP-induced secretion of phospholipase A2 (PLA2) from rat mesangial cells (IC50s = 43 and 33 nM, respectively). Tetranactin (50 ng/ml) suppresses the proliferation of human T lymphocytes induced by allogeneic cells and IL-2 and supresses the generation of cytotoxic T lymphocytes in mixed lymphocyte cultures.