In six nonatopic normal subjects, neither intravenous histamine infusion (0.3 mg.kg-1.min-1) nor intravenous propanolol (10 mg) alone produced significant change in pulmonary mechanics. Histamine infusion after propranolol resulted in an increase in pulmonary resistance (RL) from 2.1 +/- 0.41 (mean +/- 1 SE) to 3.3 +/- 0.76 cmH2O./-1.S-1 (P greater than 0.05); maximal flow at 50% total lung capacity (Vmax 50) decreased from 3.6 +/- 0.35 to 2.7 +/- 0.44 l/s (P greater than 0.01). Similar changes in Vmax 50 were observed during partial forced expiratory maneuvers from end-tidal inspiration (PEFV). On 80:20 helium-oxygen mixture Vmax 50 during maximal expiration (MEFV) decreased from 4.9 +/- 0.61 to 3.4 +/- 0.61 l/s (P greater than 0.005) and during PEFV diminished from 4.6 +/- 0.61 to 2.8 +/- 0.46 l/s (P greater than 0.005). Density dependence (deltaVmax 50) decreased significantly (P greater than 0.05) during PEFV but not during MEFV. There were no significant changes in tidal pulmonary compliance, in closing volume and closing capacity (resident gas technique), and in inflation and deflation pressure-volume curves. We conclude that iv histamine in low doses constricts peripheral conducting airways in man but this effect is masked by histamine-induced release of catecholamines from the adrenal glands.