Summary A spectrophotofluorometric method for determination of plasma salicylates is described in which a dextrangel (Sephadex) filtration system is used instead of solvent extraction or protein precipitation for separation of non-protein-bound salicylate from plasma protein. This method permits rapid estimation of binding of drug to protein in addition to estimation of free, acetyl and total salicylate. At physiological pH very little salicylate is bound to the protein in dog plasma (<10%) whereas in the human, as much as 40-50% of the salicylate is bound at plasma levels of 20-25 mg%.