Conjunctival biopsy specimens from patients with Bitot's spot responsive and nonresponsive to vitamin A were studied by light and electron microscopy. In both types, the lesions demonstrated keratinization with granular cells, irregular maturation, inflammatory infiltration of the conjunctival substantia propria, and loss of goblet cells. Only in the responsive cases were these changes generalized. Prominent Bitot's spots represented massive accumulations of Gram-positive bacilli and keratin debris. Responsive cases improved histologically within seven days of treatment, and goblet cells began to return within two weeks. These results support our previous suggestions that there is little basis for attempting to differentiate, clinically, between the two types of lesions and that at least some nonresponsive lesions represent a persistent metaplastic change induced during a prior episode of vitamin A deficiency.