A partial least-squares regression (PLS) was developed for the simultaneous spectrophotometric determination of aluminum and beryllium in geochemical samples by xylenol orange as the chromogenic reagent in water media and in micellar media. The effects of pH, xylenol orange concentration and surfactant concentration on the complexes formation reactions were studied. In the absence of surfactant the complex color development takes place at 2 h after mixing the reagents. By using CTAB as micellar media the complexes formation was improved and the rate of the complexation reactions increased. By using PLS-1 algorithm satisfactory results were obtained. The proposed procedure showed to be useful for prediction of Al and Be values from 0.1 to 1.0 mg L(-1).