Two patients (a 41-year-old woman and a 40-year-old man) with macular corneal dystrophy developed significant visual impairment from recurrent disease within corneal grafts. One patient required regrafting 18 years after a penetrating keratoplasty, and the second patient underwent a penetrating graft 19 years after a lamellar corneal graft. In both cases the typical histochemical and electron-microscopic features of macular dystrophy were evident within donor tissue from the original grafts. The patient who originally underwent penetrating keratoplasty had recurrent disease in the corneal endothelium and within Descemet's membrane. Although the explanation of this observation is uncertain, endothelial cells of the recipient human cornea may resurface Descemet's membrane after penetrating keratoplasty, contrary to current belief. An alternative possibility is that involvement of both the corneal endothelium and Descemet's membrane in macular dystrophy is a secondary phenomenon, and that the abnormal storage product of this dystrophy is an abnormal metabolite rather than a normal compound with a defective catabolic enzyme as previously suspected.