Vital staining with the fluorescent dye, acridine orange, was evaluated as a means of detecting abnormalities of lysosomes in cultivated fibroblasts of patients with macular corneal dystrophy and mucopolysaccharidoses types I-H (Hurler's syndrome) and type II (Hunter's syndrome). Multiple cultures were compared with normal fibroblasts using a "double-masked" design to exclude observer bias. Cells of patients with the mucopolysaccharidoses were easily and accurately separated from other fibroblasts. Contrary to a recent report, corneal fibroblasts of patients with macular corneal dystrophy were indistinguishable from control cells.