The effectiveness of continuous negative pressure (CNP) and nasal continuous positive airway pressure (CPAP) in the treatment of hyaline membrane disease and the incidence of complications were compared in 36 preterm infants randomly treated with CNP or nasal CPAP. Both methods of treatment were effective in increasing PaO2 and allowing a decrease in inspired O2 concentration. The time required with mechanical assistance and with an O2 concentration of more than 40% was equal in both groups. In the CNP group, four infants required mechanical ventilation because of clinical deterioration whereas in the nasal CPAP group, seven needed this type of therapy. Three infants in each group had extraalveolar air, and two patients in each group died. The results suggest that both methods of applying continuous distending airway pressure are effective. Nasal CPAP has the advantages of easier application and better access to the infant.