A near infrared spectroscopic method for the simultaneous determination of the active principles paracetamol, ascorbic acid, dextrometorphan hydrobromide, caffeine and chlorpheniramine maleate in a pharmaceutical preparation was developed. The five active principles are quantified using a partial least-squares regression method (PLS1). The proposed method is applicable over a wide analyte concentration range (0.04-6.50 wt.%), so it requires careful selection of the calibration set. Also, there is the difficulty of ensuring thorough homogenization of the product. The method was validated in accordance with the ICH standard and the EMEA validation guidelines for NIR spectroscopy by determining its selectivity, linearity, accuracy, precision and robustness. Based on the results, it is an effective alternative to existing choices (HPLC and redox titrimetry) for the same purpose. (C) 2005 Elsevier B.V. All rights reserved.