β₂AR-OE mice have increased contractile responses in airway smooth muscle. Tracheal rings from the β₂AR-OE mice and wild-type littermates were contracted by the indicated concentrations of acetylcholine (ACh). The overall responses differed (P < 0.001 by ANOVA), and the maximal response was approximately 33% greater for the β₂AR-OE rings (P < 0.001). Results are from six experiments. P values of individual post hoc comparisons: *P = 0.02; **P < 0.001.