This double-blind placebo-crossover study examined the effect of nedocromil sodium, 4 mg aerosol 30 min before challenge, on exercise-induced bronchoconstriction (EIB) in cold air conditions. Twenty-one asthmatic patients (15-28 years), with methacholine PC20 < or = 8 mg/ml in the absence of significant allergen exposure, were randomized to active and placebo therapy on separate study days. Pulmonary function, measured up to 20 min after exercise, showed significantly less deterioration with nedocromil sodium, which effectively halved the maximum percentage decline in forced expiratory volume in the first second. EIB was increased by cold air, whereas an ancillary study in 15 healthy volunteers (18-19 years) showed no such effects. We conclude that prior inhalation of nedocromil sodium diminished cold air-exacerbated EIB in young adult asthmatic patients.