• A patient with macular corneal dystrophy who had a successful 6-mm corneal transplant 23 years ago underwent a second keratoplasty for marked irregular astigmatism. The excised button, which contained the original graft and a rim of host cornea, was divided into several portions. One portion was examined histologically, another portion was incubated in organ culture with radioactive precursors and the biosynthetically labeled products characterized, and a third portion was used for cell culture and karotype analysis. The results indicated that host stromacytes had not invaded the graft and that graft stromacytes had synthesized normal proteoglycans. Furthermore, although there was excessive synthesis of abnormal proteoglycan by host stromacytes and accumulation of this material in the host cornea, minor amounts of this material actually accumulated in the graft cornea, possibly contributing to the astigmatism. A large transpant that would leave a minimum of host corneal tissue may be conducive to a longer-term good result in patients with macular corneal dystrophy.