A rapid second-derivative spectrophotometric assay procedure has been described for the determination of some benzenoid drugs in pharmaceutical dosage forms. Spectral interference from formulation excipients in simple uv spectrophotometric methods has been eliminated by the application of the proposed method. The different assay parameters, linearity and precision of the method have been assessed. The assay results obtained for eight batches of the pharmaceutical formulations of these drugs are in accord with the declared amounts. The high specificity, ease and simplicity offered by second-derivative spectrophotometry permit unit dose assay of these formulations.