The effect of large doses of salbutamol (S) and ipratropium bromide (IB) were tested in a double-blind, randomized, crossover study. Nine patients with cystic fibrosis (CF), aged 12.8 +/- 2 years (mean +/- SE), were studied for 8 h on 2 separate days. Pulmonary function tests (PFTs) included spirometry (FEV1), lung volumes (FRC), and airway resistance (Raw) measured by body plethysmography. Heart rate (HR) and oxygen saturation (SaO2) were measured before each test. On 1 day patients received S 200 micrograms, S 400 micrograms, and IB 80 micrograms, by inhalation at 45-min interval (sequence A). On the other day, the sequence was IB 80 micrograms, S 200 micrograms, and S 400 micrograms (sequence B). The PFTs were obtained at baseline, 45 min after each inhalation, and 4 and 8 h after baseline measurements. Baseline PFTs (mean +/- SE) were not significantly different on the 2 study days (FEV1, 1.48 +/- 0.1 vs 1.42 +/- 0.1 L; FRC, 2.77 +/- 0.6 vs 2.87 +/- 0.6 L; Raw, 4.04 +/- 0.2 vs 4.00 +/- 0.3 cm H2O/L/s). The FEV1 and Raw improved from baseline after each inhalation, and at 4 and 8 h during both days (p < 0.05). Forty-five minutes after S 200 micrograms, plus S 400 micrograms, FEV1, FRC, and Raw were not significantly different compared with the values 45 min after IB 80 micrograms, plus S 200 micrograms (1.67 +/- 0.1 vs 1.63 +/- 0.1 L; 2.81 +/- 0.6 vs 2.65 +/- 0.5 L; and 2.98 +/- 0.2 vs 2.66 +/- 0.1 cm H2O/L/s, respectively). The PFTs were not significantly different after maximal doses of IB (80 micrograms) compared with S (600 micrograms). The HR and SaO2 were not significantly different from baseline throughout the study period. These results indicate that both single and sequential therapy have a similar acute bronchodilator effect provided that large doses are used. We speculate that adrenergic and muscarinic pathways are equally important in airflow obstruction in patients with CF.