1. The long-acting beta 2-adrenoceptor agonist, salmeterol has been evaluated for its anti-inflammatory effects in the guinea-pig lung and skin. 2. Salmeterol, administered in bronchodilator doses to conscious guinea-pigs by both oral (0.01-1.0 mg kg-1) and inhaled (nebulizer concentration, 0.001-1.0 mg ml-1) routes, inhibited histamine-induced plasma protein extravasation (PPE) into the airway lumen. 3. Inhibition of PPE by salmeterol was long-lasting (greater than 6 h) and was inhibited by prior administration of propranolol (1 mg kg-1, s.c.), indicating an effect mediated by beta-adrenoceptors. 4. Inhaled salbutamol (nebulizer concentration, 0.001-1.0 mg ml-1) also inhibited PPE in guinea-pig lung but, in contrast to salmeterol, this effect was short-lived with substantial loss of activity 2 h after administration. 5. Inhaled salmeterol (0.1 mg ml-1) and salbutamol (1.0 mg ml-1) inhibited the accumulation of neutrophils in guinea-pig lung in response to lipopolysaccharide (100 micrograms ml-1). Salmeterol, but not salbutamol, inhibited the infiltration of eosinophils into the airway lumen in response to platelet activating factor (100 micrograms ml-1). These effects of salmeterol were blocked by prior administration of propranolol (5 mg kg-1, s.c.), indicating that they were also beta-adrenoceptor-mediated. 6. Oral salmeterol (10 mg kg-1, p.o.), but not salbutamol (10 and 100 mg kg-1, p.o.), inhibited zymosan-induced granulocyte accumulation and PPE in guinea-pig skin. Lower doses of salmeterol (0.1 and 1 mg kg-1) inhibited PPE, but not granulocyte accumulation.The effects of salmeterol were blocked by prior administration of propranolol (1mgkg-', s.c.). Both salmeterol and salbutamol inhibited histamine-induced PPE in guinea-pig skin.7. Intradermal salmeterol (10-'mol per site), but not salbutamol, was also effective in inhibiting zymosan-induced granulocyte accumulation and PPE in guinea-pig skin.8. It is concluded that salmeterol, at bronchodilator doses in the guinea-pig, inhibits granulocyte accumulation and PPE, possibly by an action on the vasculature. As this profile of activity is not shared by the shorter-acting compound, salbutamol, it would seem that anti-inflammatory activity is associated with beta-adrenoceptor agonism of long duration. The implications of these findings for the use of salmeterol in the treatment of bronchial asthma are discussed.