The efficacy and safety of nedocromil sodium inhalation aerosol (4 mg of Tilade administered by metered-dose inhaler) given twice daily was compared with placebo in 112 patients with mild-to-moderate asthma who had been receiving maintenance therapy with oral or inhaled bronchodilators or both. After a 2-week run-in period and a subsequent 2-week baseline period, patients were randomized to active treatment (n = 56) or placebo (n = 56) for 8 weeks. All maintenance bronchodilators were withdrawn before the baseline period, and patients entered the treatment period only after demonstrating a specified level of asthma symptoms. Twice daily administration of nedocromil sodium improved all asthma symptoms in these patients who had symptoms as a result of the withdrawal of their maintenance theophylline and/or oral and inhaled beta 2-agonist bronchodilators. During the primary time period (treatment weeks 5 to 8), statistically significant between-group differences favored nedocromil sodium for the asthma summary score (primary variable, p = 0.001), daytime asthma (p = 0.001), and sleep difficulty caused by asthma (p = 0.006). Furthermore, significant reductions in the use of as-needed rescue medications were reported in the nedocromil sodium group (p = 0.003) compared with the placebo group. Final overall opinions of treatment effectiveness expressed by physicians (p = 0.016) and patients (p = 0.002) strongly favored nedocromil sodium.