PURPOSE To identify the underlying mutations in two unrelated British families with macular corneal dystrophy (MCD) by screening the carbohydrate sulfotransferase (CHST6) gene. DESIGN Case reports and results of DNA analysis. METHODS Two subjects from two British families with MCD were studied. The genetic status of CHST6 was determined for all members of these MCD families. In addition, sulfated keratan sulfate (KS) assay from the probands was also undertaken. CHST6 gene was amplified by polymerase chain reaction (PCR). The PCR products were analyzed by sequencing and restriction digestion. Enzyme-linked immunosorbent assay (ELISA) was performed to assess KS presence in serum. RESULTS Four compound heterozygous mutations were identified, three of which are novel. The ELISA showed that the probands were of MCD type I. CONCLUSIONS These novel mutations are expected to result in loss of CHST6 function, which would account for the MCD phenotype.