SummarySurfactant‐deficient premature newborn rabbits obtained by hysterotomy on day 27 of gestation were tracheostomized at birth, kept in a multichambered pressure‐constant body plethysmograph, and subjected to intermittent positive pressure ventilation using a standardized insufflation pressure (30 cm H2O). A sequence of various frequencies (20, 40, and 60/min) and inspiration:expiration (I:E) ratios (1:4, 1:2, 1:1, 2:1, and 4:1) were applied, and the effect of these various respirator settings on tidal volume (VT) and flow was evaluated by means of a Fleisch tube connected to the body plethysmograph. Irrespective of respirator frequency, increasing I: E ratio from the basic setting of 1:1 resulted in increased VT; decreasing I:E ratio had the opposite effect. There was a nearly linear relation between variations in I:E ratio and VT, but the slope of the regression line was steeper at frequencies 40 and 60/min than at 20/min. At a frequency of 20/min, values (X ± S.D.) for lung‐thorax compliance at I:E ratios of 1:4 and 4:1 were 0.50 ± 0.26 and 0.99 ± 0.42 ml/cm H2O·kg, respectively. Corresponding figures for frequency of 60/min were 0.21 ± 0.10 and 0.73 ± 0.36 ml/cm H2O·kg. At the two higher frequencies and low I:E ratios (≤1:1), the duration of the inspiration phase was not sufficient to provide the maximal degree of lung expansion attainable with this insufflation pressure under static conditions. At frequency of 60/min and I:E ratio of 4:1, the expiration was short enough to prevent zero flow before onset of inspiration.SpeculationThe wet lungs of premature neonates with surfactant deficiency are not ventilated effectively with a conventional inspiration:expiration ratio of 1:1, or less. However, by increasing inspiration: expiration ratio to as much as 4:1, the viscosity of the fluid in the airways can be overcome, and the lungs can then be ventilated with a lower insufflation pressure. This alternative setting of the respirator should reduce the risk of long‐term complications, such as bronchopulmonary dysplasia, in surfactant‐deficient babies treated with artificial ventilation in the neonatal period.