Respiration, as judged by gas exchange and pulmonary function, is improved in preterm infants kept in the prone rather than the supine position. The influence of position on the breathing pattern as documented by the pneumogram was studied in 14 stable preterm infants with recent clinical apnoea. Ten of the infants had oximetry and nasal flow studies simultaneously with the impedance pneumogram. Each infant had consecutive nocturnal pneumograms, one in the prone, one in the supine position. The infants were kept for more than six hours in the assigned position.A significant increase in apnoea density and in periodic breathing was found in the supine v the prone position (mean (SE) 4-5 (0O7)% v 2-5 (0O5)%, and 13-6 (3-2)% v 7-7 (2-2)%, respectively). There was no positional difference in the incidence of bradycardia and prolonged apnoea. The examination of obstructive apnoea, mixed apnoea, and cyanotic spells did not reveal a consistent disparity between the two positions.These findings indicate an increase in central apnoea in preterm infants kept predominantly in the supine position. Possible relations of positional changes to lung mechanics are discussed. When evaluating pneumograms, attention must be given to the position in which they were performed. (474) g, range 840-2290 g) who had recent clinical apnoea but were otherwise healthy were enrolled in the study, after informed consent was obtained from the parents. Nine infants had previous respiratory distress syndrome requiring up to eight days of intubation. Infants with bronchopulmonary dysplasia were excluded from the study. The infants did not require respiratory support or oxygen, and were all enterally fed (bolus feedings either by nipple or by intermittent gavage) at the time of the study. Eight infants received maintenance methylxanthine therapy and had stable therapeutic blood concentrations.The breathing pattern was studied by the cardiorespirogram (pneumogram). Each infant had consecutive nocturnal 12 hour impedance pneumograms: one while in the prone and one in the supine position. The order was assigned at random, by sealed envelopes. When assigned to the prone position, infants were kept in the assigned position all night, except during feeding. When assigned to the supine position, infants were kept supine except for one hour after feeding, when they were placed prone to facilitate burping and prevent aspiration. The infants spent the majority of the study period in the assigned position. No attempt was made to keep the head in midline position. In general, the head was turned to the side 75-90°when prone and about 450 when supine. The infant's neck and shoulders were supported to avoid neck flexion.Pneumograms were analysed using a Pediatric Diagnostic Service computer program, as developed by Kelly et al.6 Apnoea episodes were defined as cessation of breathing for ¢s6 seconds.