Two patients with Best's macular dystrophy, photographically documented, developed vitelliform lesions in previously normal or nearly normal fundi. The patients were studied prospectively because their brother had Best's disease. The first patient, a 6-year-old boy, had normal-appearing fundi in February 1974, but in October 1974 he had developed a vitelliform lesion in the left macula. His electro-oculogram (EOG) was severely abnormal in both eyes. His 12-year-old syster had an essentially normal fundus appearance and an abnormal EOG in both eyes in November 1971. In October 1975, she had an extramacular vitelliruptive lesion in the right eye and a typical Best's lesion in the left macula.