We compared the inhibitory effects of inhaled salbutamol (S), ipratropium (I), and cromoglycate (C) on bronchospasm induced by exercise (EX) or hyperosmolar (HY) saline aerosol in a group of 11 subjects with stable asthma. Each subject had eight tests in a randomized order, four EX and four HY challenges, each preceded by the double-blind inhalation of either a placebo, 200 micrograms of S, 80 micrograms of I, or 4 mg of C. This study demonstrated that the three drugs protected against the two types of challenges in almost all subjects. Although we observed a large interindividual variability in the airway response to the challenges, there was no statistically significant difference in the mean percent protection after HY or EX challenges when these challenges were preceded by S, I, or C (p greater than 0.05). Moreover, for EX- and HY-induced bronchospasm, the mean percent protection afforded by the three medications was in the same order (S greater than I greater than C), although the protective effect against EX-induced was weaker than against HY-induced bronchospasm. This suggests that hyperosmolarity, although it may not be the sole factor involved, plays a role in EX-induced bronchospasm.