Thirty dogs with chronic superficial keratitis (CSK) were randomly assigned to treatment with 0.2 per cent cyclosporin ointment or 0.1 per cent dexamethasone drops. They were treated for six weeks and examined before and after three and six weeks of treatment, and then every three weeks without treatment until the lesions recurred. The regression of the disease during the treatment and the time to a recurrence after the cessation of treatment were determined. Changes in the size of the corneal lesions were measured by image analysis of photographs taken at each examination, and the severity of adnexal changes such as conjunctival hyperaemia was assessed by means of a scoring system. Clinical evaluations suggested that both drugs were equally effective as treatments for CSK and a statistical analysis showed that they had reduced the size of the lesions to the same extent at each examination. There was a significant increase in tear production, measured by the Schirmer tear test, during the treatment with cyclosporin.