Cardiorespiratory measures are used with increasing frequency to assess individual differences in development in full-term and preterm infants, yet little information exists concerning the stability of these measures or their relations to each other. This study assessed three common cardiac measures (heart period, heart period variability, and vagal tone) and two measures of arterial oxygenation based on pulse oximetry (mean pulse oxygen saturation and variability) in a sample of 35 preterm infants. Data were collected on five occasions: on 3 consecutive days in the early neonatal period, at 34 weeks postconceptional age, and at discharge. Results indicate both short-term and longer term stability for all cardiac measures. Oxygen saturation demonstrated only short-term stability prior to 34 weeks. Mean heart period was positively associated with both measures of heart period variability at each assessment point, while mean oxygen saturation level was inversely related to oxygen saturation variability. In addition, significant associations between cardiorespiratory patterns and perinatal risk measures were found. It is concluded that these measures reflect stable characteristics of neuroregulatory function in preterm infants.© 1994 John Wiley & Sons, Inc.