Vitamin A deficiency causes blindness, increased systemic morbidity, and increased mortality among preschool children in many developing nations. Presently, there is no simple, reliable test to detect early, physiologically significant vitamin A deficiency. We used conjunctival impression cytology results to evaluate children with early xerophthalmia before treatment and again three to eight weeks later. Subsequently, we modified our technique. We then compared children with early xerophthalmia to normal children. Conjunctival impressions from children with xerophthalmia all showed complete loss of goblet cells and the appearance of enlarged, partially keratinized epithelial cells. Conjunctival impressions from treated and normal children showed normal goblet cells and sheets of small epithelial cells. These results suggest impression cytology may represent the first simple, objective, diagnostic test for the detection of early vitamin A deficiency.