Using the modified bidimensional electrophoresis method, characteristic patterns of urinary glycosaminoglycans were obtained for nine different syndromes of mucopolysaccharidoses and normal. Each pattern, portrayed on a 55 mm square cellulose acetate membrane, was visualized by staining the electrophoretically separated GAGs with alcian blue. The method, tested with 38 cases, was precise and sensitive; the first direction of electrophoresis was run for 25 min and the second direction for 60 min. Because the method is qualitative, the usual quantitative measurements and calculations are circumvented. Moreover, any irregular pattern can readily be verified by repeating the bidimensional electrophoresis. Thus, the clarity of the pattern itself offers assurance of its diagnostic reliabilty; consequently, false negative and false positive results should be minimized.