The purpose of this study was to compare the effects of prone and sitting on the heart rates, respiration rates, and arterial oxygen saturation levels of premature infants. The positioning device used for sitting the infants was the premature infant seat, an experimental seat developed by the principal investigator. Thirty premature infants' heart rates, respiration rates, and arterial oxygen saturation levels were recorded in three 30-minute periods: 1) prone-baseline, 2) sitting in the premature infant seat, and 3) pronerecovery. One-way analysis of variance revealed statistically significant results for the effect of position change (p< .05). The difference between the infants' mean group values for the effect of position change on the dependent variables showed little clinical change between prone and sitting. No episodes of apnea or bradycardia occurred during the study. The results of this study suggest that sitting in the premature infant seat should be considered an alternative position to prone for clinically stable premature infants. © 1990 by Williams and Wilkins.