Synthetic surfactant peptides offer an opportunity to standardize the protein composition of surfactant. We tested the effect of phospholipids (PL) with synthetic full-length SP-B1-78(B), mutant B (Bser), KL4peptide (UCLA-KL4), and palmitoylated SP-C1-35(C) on oxygenation and lung function in a surfactant-deficient rat model. Sixty-four adult rats were ventilated with 100% oxygen, a tidal volume of 7.5 mL/kg, and a rate of 60/min. Their lungs were lavaged with saline until the arterial PO2dropped below 80 torr, when 100 mg/kg surfactant was instilled. Surfactant preparations included: PL (PL surfactant), PL + 3% B (B surfactant), PL + 3% B and 1% C (BC surfactant), PL + 3% UCLA-KL4(KL4surfactant), PL + 3% Bser (Bser surfactant), and PL + 3% B and 1% UCLA-KL4(BKL4surfactant). Sixty minutes after surfactant instillation, positive end-expiratory pressure was applied for 5 min, and pressure-volume curves were determinedin situ. The six surfactant preparations had a minimum surface tensions <10 mN/m on a Langmuir/Wilhelmy balance. Instillation of PL, Bser, and BKL4surfactant increased mean arterial/alveolar PO2(aADO2) ratios by 50-100% over postlavage values, whereas KL4surfactant increased aADO2ratios by 118%, B surfactant by 191%, and BC surfactant by 225%. Lung volumes at 30 cm H2O pressure were highest after treatment with BC surfactant, intermediate after B and KL4surfactants, and lowest after BKL4, Bser, and PL surfactants. These data suggest that a surfactant preparation with a combination of synthetic B and C peptides surpasses synthetic B and KL4surfactants in improving oxygenation and lung compliance in surfactant-deficient rats.Abbreviations: aADO2,arterial/alveolar PO2ratio;DPPC,dipalmitoyl phosphatidylcholine;FIO2,fraction of inspired O2;PA,palmitic acid;Pao,arterial partial pressure of O2;PaCO2,arterial arterial partial pressure of CO2;PEEP,positive end-expiratory pressure;PL,phospholipid;POPG,1-palmitoyl-2-oleoyl phosphatidyl glycerol;SP,surfactant protein;PG,phosphatidyl glycerol;Fmoc,N-(9-fluorenyl)methoxycarbonyl