Arterial oxygen tension and functional residual capacity were studied in 16 intubated, spontaneously breathing newborn infants recovering from respiratory disease. Studies were made at 2 cm H2O continuous positive airway pressure, at zero end expiratory pressure, and following extubation. The study showed that PaO2 and FRC at 2 cm H2O CPAP were the same as observed following extubation, but that both values were significantly lower at ZEEP.