We conducted a randomized, double-blind, placebo-controlled study on the effect of disodium cromoglycate (DSCG) and nedocromil sodium (NED) on propranolol-induced bronchoconstriction (PIB) in 12 asthmatic subjects 10 to 53 years of age. Placebo (saline solution) and active drugs (10 mg) were aerosolized 30 minutes before bronchoprovocation with inhaled propranolol. Bronchial response to propranolol was expressed as the cumulative dose provoking a 20% fall in FEV1 (PD20P) and given in mumol. Reproducibility of PD20P was estimated before and after the days of study. PD20P varied within two doubling doses. Disodium cromoglycate and NED had no significant effect on baseline lung function. Although, geometric mean PD20P values (+/- GSEM) recorded after DSCG (7.24 mumol +/- 1.31) and after NED (9.22 mumol +/- 1.26) were higher than values recorded after placebo (6.55 mumol +/- 1.31), these differences were not statistically significant. A greater than 2-fold increase in PD20P was noted after NED in three subjects and in one subject after DSCG. We conclude that both DSCG and NED only modestly alter PIB, with some between subject differences.