Increased airway resistance in asthma may be partly due to poor function of pulmonary surfactant. This study investigated the inflammatory changes of bronchoalveolar lavage fluid (BALF) and the performance of BALF surfactant in healthy control subjects (n = 9) and patients with mild allergic asthma (n = 15) before and after segmental challenge. BALF was obtained for baseline values, and 24 h after challenge with saline solution in one lung segment and with allergen in another. Cell counts, phospholipid and protein concentrations, and ratios of small to large surfactant aggregates (SA/LA) were analyzed. Surface tension was determined with a pulsating bubble surfactometer, and the ability of the BALF surfactant to maintain airway patency was assessed with a capillary surfactometer. Baseline values of control subjects and asthmatics were not different. Challenge with saline and antigen raised total inflammatory cells in both control subjects and asthmatics. Allergen challenge of asthmatics, but not of healthy volunteers, significantly increased eosinophils, proteins, SA/ LA, and surface tension at minimum bubble size, and diminished the time the capillary tube is open. In conclusion, allergen challenge in asthmatics induced surfactant dysfunction, probably mainly because of inhibiting proteins. During an asthma attack, narrow conducting airways may become blocked, which might contribute to an increased airway resistance.