The permeability of phospholipid spherules to 11 anions was examined by measuring volume alterations under conditions in which these alterations reflect changes in anion movement. Chloride and bromide cross the membrane by some type of electrically neutral process not involving the species HCl or HBr. By comparison, iodide, thiocyanate, and salicylate are permeable in the charged form. Furthermore, the transport of these three anions is reduced by incorporation of cholesterol into the bilayer structure; iodide being affected more than thiocyanate or salicylate. Formate, acetate, propionate, benzoate, p-hydroxybenzoate, and p-aminobenzoate all permeate as undissociated acids. The relative permeabilities of these anions correlate well with organic solvent – water partition coefficients. Salicylate (o-hydroxybenzoate) can penetrate both in the undissociated and dissociated states. As opposed to the other aromatic anions, salicylate is capable of adsorbing to the lipid membrane in the ionic form. This property may partially explain the ability of this benzoate derivative to traverse the membrane as an ion. Salicylate can also facilitate the movement of anions such as acetate by virtue of its ability to make the lipid bilayer more permeable to hydrogen ions.