The morphology and histochemical attributes of the lesions in macular corneal dystrophy have been well characterized and thus far found to be restricted to the cornea. This inherited metabolic storage disease is thought to be a localized mucopolysaccharidosis and an enzymatic defect in the degradation of corneal keratan sulphate is suspected. Studies on cell cultures of fibroblasts from diseased corneas have as yet failed to extend our knowledge about the pathogenesis of the disorder. Such investigations have included the use of acridine orange and metachromatic dyes, assays for lysosomal enzymes, biochemical analyses of cells and media, as well as kinetic studies on the synthesis and degradation of radioactive glycosaminoglycans. Despite the lack of supportive evidence, the cell culture data nevertheless remain consistent with the hypothesis that macular corneal dystrophy is a disorder of keratan sulphate I catabolism, since the synthesis of keratan sulphate by corneal fibroblasts normally decreases markedly in culture. Studies on corneal explants with macular dystrophy have provided significant positive information about this dystrophy. Freshly excised corneas with macular dystrophy synthesize considerably less keratan sulphate than normal corneas, while they produce excessive amounts of glycopeptides which still need to be characterized.