Ten patients with oral leukoplakia were treated topically with bleomycin. We found the method convenient but only successful where sufficient attention was paid to the activity of the bleomycin-dimethylsulphoxide solution. The initial epithelial dysplasia disappeared completely in five of the 10 patients, while in the remainder the dysplastic grade remained the same. Following treatment the thickness of the keratotic layer increased in four patients, became thinner in five and remained unchanged in one. Although clinically the results of treatment only appear some 3 months after bleomycin application, once the lesions are cured their recurrence seems to be slower than after surgery. Nevertheless we strongly emphasise that 3-monthly follow-ups are mandatory for patients with oral leukoplakias whether or not they have been treated successfully.