Abstract 1. 1. The leukotriene C 4 (LTC 4)-induced contraction and thromboxane A 2 (TxA 2) release of the guinea pig lung parenchymal (GPLP) strip are both inhibited by the β 2-adrenergic agent salbutamol. The effect of LTC 4 is restored to nearly normal by the β-adrenergic antagonist sotalol. 2. 2. The latter substance alone also induces a contraction in the GPLP strip and potentiates the contractions and the TxA 2 release of LTC 4. During the sotalol-induced contractions, no TxA 2 release occurs. An antihistaminic, mepyramine had no effect on the sotalol-induced contraction. 3. 3. When sotalol is added repeatedly to a GPLP strip, only the first time a contraction occurs.