The alterations in the conjunctival epithelium during the course of vernal conjunctivitis were examined by conjunctival impression cytology. The study was carried out on 53 patients with vernal conjunctivitis and 20 normal subjects as control. The results of impression cytology demonstrated that all cytological parameters were significantly modified in vernal conjunctivitis patients; the earliest alterations were found in the distribution of goblet cells, in the intercellular junctions, in the chromatin morphology and in the degree of keratinisation. The morphometric comparison showed that in vernal conjunctivitis patients the mean number of goblet cells per field was significantly higher than in controls. Moreover the mean diameter of goblet cells was smaller in patients than in controls. Impression cytology can, therefore, be a simple, non-invasive and cheap method for the study of the ocular surface in vernal conjunctivitis.