Surfactant-deficient ventilated preterm lambs were treated with 100 mg/kg of surfactant radiolabeled with microspheres at 30 min and 2.5 h of age to evaluate the effect of treatment technique on surfactant distribution. The treatments were four positions with four boluses (bolus 4), two lateral positions with two boluses (bolus 2), or a 30-min infusion (infusion). The bolus groups had uniform surfactant distributions to the > 100 pieces analyzed for each lung. Infusion resulted in a very nonuniform surfactant distribution (P < 0.01). Surfactant was recovered equivalently in all lobes of the bolus groups, whereas infusion lungs contained surfactant preferentially in upper lobes (P < 0.01). The second dose of surfactant localized into the same lung doses as the first dose (P < 0.001). Blood flow increased proportionately to surfactant content in the bolus groups. With infusion, blood flow decreased and ventilation measured with 99Tc-labeled aerosol increased to pieces of lung receiving large amounts of the infusion surfactant, suggesting that localized overinflation was likely. Physiological measurements indicated better responses to bolus treatments, although the infusion lambs did improve. These results indicate that different treatment techniques can have large effects on surfactant distributions.