Abstract: A new solution of simultaneous equations in spectrophotometry is studied. Owing to replacing the absorption coefficients by the absorption ratios, the authors have obtained rather greater accuracy from Vierordt's method than hitherto. A further development of the same formulation has led to a simple theoretical criterion, which enables the analyst to avoid pairs of wavelengths that are unsatisfactory for precision.This new method has been applied to the assay of compound injection of sodium benzoate and caffeine and compound tablet of amidopyrine and caffeine with satisfactory results.