The equation that express the combined effect of the organic modifier content and mobile phase pH has been used to predict the chromatographic behavior of flurbiprofen, ibuprofen, diclofenic acid, ketoprofen, fenoprofen, naproxen, bezafibric acid and clofibric acid. Correlations between the retention factors of the solutes and pH of the mobile phase were determined from a set of 40 chromatograms for each compound at four different levels of acetonitrile composition (40, 45, 50 and 55 %, v/v), and at ten pH values in each acetonitrile-water mixtures. In this way, a complete description of the retention behavior of each solute in the space defined by the pH and organic modifier percentages variables was obtained. The optimized chromatographic condition was applied to quantitative determination of flurbiprofen, ibuprofen, and diclofenic acid in pharmaceutical dosage forms.