Impression cytology was used to study the ocular surface of 32 eyes with keratoconjunctivitis sicca. Among these eyes, on the basis of the results of the Schirmer I test, two groups of eyes have been identified. The first group with Schirmer test less than 5.5 mm/5 min showed decreased concentration of goblet cells and increased cytoplasm/nucleus ratio on all the areas of the bulbar conjunctiva. The second group, with Schirmer test greater than 5.5 mm/5 min, showed similar changes to be localized in the interpalpebral bulbar conjunctiva only, while the eye surface protected by the lids was almost normal. These observations suggest a pathogenetic role of tear evaporation in eyes with tear film instability even in the presence of a 'theoretically' normal tear production.