A double-blind, randomized, crossover chronic study was done to determine the efficacy of colchicine in 10 atopic patients with asthma. A constant dose of sustained-release theophylline and albuterol by inhalation, as needed, was administered. Compared to placebo, colchicine, 0.5 mg twice daily, significantly reduced the mean (+/- SEM) daily clinical score from 2.18 +/- 0.34 to 1.64 +/- 0.32 (p less than 0.05), and the daily number of inhalations of albuterol from 5.89 +/- 1.48 to 4.01 +/- 1.26 (p less than 0.02). Colchicine significantly (p less than 0.05) increased the concanavalin A-induced suppressor cell function from 16.2 +/- 4.6% to 39.0 +/- 10.7%, which was similar to healthy volunteers (41.1 +/- 3.5%). Furthermore, colchicine significantly (p less than 0.05) decreased serum IgE from 248 +/- 63 to 188 +/- 46 IU/ml. Colchicine had no significant effect on pulmonary function tests, the early phase reaction of antigen-induced bronchial inhalation challenge, and immediate skin test responses. Thus, colchicine has immunomodulatory effects that may perhaps have a mild benefit in the treatment of asthma.