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Three simple and sensitive visible spectrophotometric methods (A–C) are described for the assay of vancomycin (VCM) and dobutamine (DB) (in pure form and in pharmaceutical formulations). These methods are based on the oxidation of vancomycin or dobutamine with excess sodium metaperiodate. Either the products formed (liberated aldehyde with 3-methyl-2-benzothiazolinone hydrazone (MBTH), method A; iodate with p-methylaminophenol sulphate (PMAP), sulphanilamide, in the presence of Mo (VI), method B) or the amount of periodate consumed (celestine blue in the presence of tellurium (IV), method C) are estimated. In this paper the reaction mechanism is presented and all the variables are optimized. Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 2.5–30, 0.6–6.0; 2–24, 0.8–9.6 and 2–24, 0.76–6.0 µg ml−1 for methods A, B and C of VCM and DB respectively. The validity of the proposed methods was tested by analyzing pharmaceutical formulations containing drug (VCM, DB) and the relative standard deviations were within 1.0%. Recoveries are 99.55–99.94%.