Dimethylsulfoxide and three related sulfoxides exhibit some of the biochemical properties of classical non steroidal antiinflammatory acidic drugs. Thus n-propyl sulfoxide, n-butyl sulfoxide and tetramethylene sulfoxide stimulate 02 consumption by rat liver mitochondria. These 3 compounds induce mitochondrial swelling. Lymphocyte swelling is only induced by high doses of n-propyl sulfoxide and n-butyl sulfoxide and not by tetramethylene sulfoxide.These suffoxides induce changes in membrane permeability of various lymphocytes to ions by increasing 45Ca, 86Rb, 134Cs and 22Na fluxes across these membranes, the direction and the magnitude of which are dependent on the ionic composition of the medium and sulfoxide concentration.They all inhibit the incorporation of 3H-thymidine, aH-uridine and 14C-aminoacids into lymphocytes DNA, RNA and proteins.The relevance of such biochemical properties for analgesic or antiinflammatory clinical effects is discussed.