In order to identify early and late modifications induced by ionizing radiation on the conjunctival surface, we studied 10 patients irradiated for paranasal sinus tumors. A clinical and morphological study of conjunctival epithelium (using an impression cytology technique) was performed; 5 patients were examined during and the others after treatment. Actinic conjunctivitis and keratitis, observed during treatment, reappeared within a few months after the end of radiotherapy. At a threshold dose of 25 Gy, chronic nuclear changes and cellular surface disorganization of the conjunctival epithelium were found--these progressed and persisted. Our data support the importance of careful monitoring of such irradiated patients and the benefit of planning a prospective clinical study to evaluate the effects of available drugs (all-trans retinoic acid) in the treatment of these lesions.