Relatively few morphological studies on human cornea have been performed due to the difficulty in obtaining material. The specimens may be obtained either by superficial scraping-off, limited to the epithelial layer, or from corneal buttons obtained at keratoplasty. Conjunctiva, on the other hand, may be obtained by painless biopsy. We have studied the three-dimensional ultrastructure of the normal cornea and conjunctiva and in the course of various diseases where the application of scanning electron microscopy (SEM) seemed to be useful. In the cornea, we studied Fuchs' endo-epithelial dystrophy. In the conjunctiva, we analysed the ultrastructural characteristics of adenovirus follicular conjunctivitis, hay fever conjunctivitis and keratoconjunctivitis sicca. We also considered the problem of contact lens wearing, studying by SEM both the conjunctival tissue and the discarded lenses. On the basis of our results we conclude that SEM supplies useful information which integrates that obtained by biomicroscopy, used by clinicians to interpret the lesions at microscopic level. It is, however, indispensable to carry out, in addition to SEM, an examination on sections to completely investigate the disease.