The serum of most patients with type 1 macular corneal dystrophy (MCD), the most prevalent subtype, lacks detectable antigenic keratan sulfate (KS), and it has been postulated that such individuals may lack antigenic KS in their cartilage as well. To test this hypothesis, we studied the cornea, serum, and nasal cartilage from an MCD patient using light and electron microscopy, immunohistochemistry, and a quantitative enzyme-linked immunosorbent assay (ELISA) which uses a monoclonal antibody against a sulfated epitope on the KS chain to measure KS content. Histologically, corneal deposits seen were characteristic of MCD. No abnormal deposits were noted in the cartilage. The lack of immunoreactivity in corneal sections with antibodies against sulfated epitope on KS and the absence of this epitope in serum showed that the patient had type 1 MCD. The cartilage specimen showed no immunoreactivity in the chondrocytes or extracellular matrix. Quantitative analysis by ELISA demonstrated that the antigenic KS content of the cornea and cartilage was at least 800 times lower than that in normal controls. This provided direct evidence that the abnormality in the sulfation of keratan in type 1 MCD involves the cornea and cartilage.