To determine the efficacy of the mast cell-stabilizing drug ketotifen in scleroderma, we conducted a 6-month, randomized, prospective, double-blind, placebo-controlled trial in 24 patients. No significant improvement in the clinical parameters, pulmonary function, global assessments, and mast cell releasability was noted. Pruritus tended to improve in the group taking the active drug. Six months of treatment with ketotifen (6 mg/day), therefore, produced no apparent benefit in patients with early scleroderma. We were unable to address the role of mast cells in scleroderma since mast cell suppression was not achieved.