1. The effects of salmeterol, a novel long-acting beta 2-adrenoceptor agonist, have been investigated on antigen-induced mediator release from passively sensitized fragments of human lung in vitro. 2. Salmeterol was a potent inhibitor of the release of histamine (-log IC50 = 8.54), leukotriene C4 (LTC4)/LTD4 (-log IC50 = 9.07) and prostaglandin D2 (-log IC50 = 8.81). It was slightly less potent (1-3 fold) than isoprenaline, but significantly more potent (10-35 fold) than salbutamol. 3. Propranolol competitively antagonized the inhibitory effects of salmeterol on histamine release (pA2 = 8.41) and LTC4/LTD4 release, (pA2 = 8.40) indicating an action via beta-adrenoceptors. 4. The inhibitory effects of isoprenaline (20 nM) and salbutamol (200 nM) were removed after washing the lung tissue for 2 h and 4 h respectively. In contrast, the inhibitory effects of salmeterol (40 nM) were much longer-lasting, and were still evident after 20 h. 5. Salmeterol therefore exhibits potent and persistent inhibition of anaphylactic mediator release from human lung. This anti-inflammatory effect may be important for the therapeutic potential of salmeterol in the treatment of bronchial asthma.