To evaluate the effectiveness of the early application of continuous negative pressure about the thorax, 23 infants with the idiopathic respiratory distress syndrome who had adequate alveolar ventilation were assigned to early or late application of CNP. There were 11 infants in the early CNP and 12 in the late CNP group. There were no differences between the two groups with respect to birth weight, gestational age, age at admission to the study, initial FIO2 requirements, or initial PaO2, PaCo2, and AaPO2. None of the ENCP patients required mechanical ventilation, whereas four of the LCNP group did so. The FIO2 requirements were significantly less for the ECNP infants when compared to the LCNP ones. The mean duration of FIO2 requirements greater than 0.6 was 28.3 hours for those receiving ECNP and 60.7 hours for those in LCNP (P LESS THAN 0.05). This study suggests that the course of RDS may be modified by the early application of CNP.