The efficacy of squaric acid dibutylester (SADBE), a topical allergen, was investigated in the treatment of 20 patients with warts. All patients had multiple or warts recalcitrant to other therapies or hesitated to have the painful cryotherapy. The patients with warts present for a mean of 15.3 months (range 1-36) were successfully sensitized with 2% SADBE in acetone. Then the warts were treated with a 0.1 or 0.01% SADBE application once a week or every other week, so as to maintain a mild contact dermatitis. Twelve of the 20 patients (60%) were completely cured after an average of 6 applications (range 2-12). Five patients (25%) showed either a poor or no response even after 9-18 applications. Three patients (15%) exhibited contact dermatitis either at the sensitization or the treatment site. Our study shows that this therapy, although not always safe, is effective in treating warts in some patients, who either hesitate at conventional cryotherapy or have warts resistant to other therapies. The safety of this method remains to be evaluated.