Impression cytology using cellulose acetate paper has been used in various ocular surface disorders as a simple non-invasive diagnostic test. To assess its value in differentiating melanocytic tumours, 24 patients with a range of pigmented lesions of the conjunctiva were examined using this technique. Cytological and histological diagnoses were compared in 23 cases. In 73% of cases impression cytology predicted the histological diagnosis by detection of superficial atypical melanocytes and their proportion relative to benign epithelial cells. This pilot study shows impression cytology to be a useful diagnostic aid in the differentiation of pigmented tumours of the bulbar conjunctiva.