A new antibiotic, aterrimin (Lewis et al., 1953), is unstable in aqueous solution at pH 7, and insoluble at lower pH levels. Aterrimin can be dissolved in absolute alcohol and the solutions can be used satisfactorily in a cylinder-plate type of assay (Heatley, 1944). Further investigation has established that sevbral other organic solvents are nontoxic to various bacteria when used in cylinders...