Many patients with chronic idiopathic urticaria are not sufficiently controlled with histamine H(1)-receptor antagonists. Leukotriene receptor antagonists have been reported to be effective for certain cases of urticaria, although their proper application remains to be established. To study the effectiveness of montelukast, a leukotriene receptor antagonist, for the treatment of chronic urticaria that was not controlled by histamine H(1)-receptor antagonists. Twenty-five patients with chronic idiopathic urticaria were treated with 10 mg of montelukast for one week or more, without changing any precedent treatment that they were using before the study including histamine H(1)-receptor antagonists. The effectiveness of montelukast for each patient was evaluated and compared with clinical features and/or backgrounds of the patients. Twelve patients, including six who had been treated with corticosteroids, were evaluated as "markedly improved" or "improved" following treatment with montelukast. There was no statistically significant relation of the effectiveness to the complications with non-steroidal anti-inflammatory drugs (NSAIDs) intolerance, mechanical urticaria, or reactions to autologous serum skin test. However, the patients for whom montelukast was effective were younger (33.2+/-16.3 years, mean +/- SD)(P<0.05, Mann-Whitney test) and their duration of illness shorter (15.9+/-18.3 months) (P<0.005, Mann-Whitney test) than those of patients for whom montelukast was ineffective (45.9+/-15.0 years, 89.6+/-71.7 months). Montelukast may be worth trying for patients with chronic idiopathic urticaria, when the condition is not sufficiently controlled with histamine H(1)-receptor antagonists.