A screening method is described for estimation of sulfamethazine and sulfathiazole residues in swine livers. Tissues are homogenized with CHCl3-ethyl acetate (1 + 1). The drugs are extracted from the organic solvent with pH 10 carbonate buffer and back-extracted into dichloromethane, as an ion-pair with tetrabutylammonium hydroxide, without pH adjustment. Following evaporation of the solvent, the residue is dissolved in methanol, subjected to thin layer chromatography, and detected by the Bratton- Marshall reaction. Recoveries of sulfamethazine and sulfathiazole, determined by high pressure liquid chromatography, were 50.8 and 42%, respectively, with coefficients of variation of 4.2 and 4.7%.