Transcutaneous oxygen pressure (tcPO2) and body temperature were monitored for the duration of feeding sessions in five small preterm infants who served as their own controls for bottle-feeding (BoF) and breast-feeding (BrF). Longitudinal data were collected twice weekly for BoF and BrF sessions from infants' first oral feeding until discharge, for a total of 71 feeding sessions: 32 BoF and 39 BrF. Markedly dissimilar for the two feeding methods, tcPO2 patterns suggested less ventilatory interruption during BrF than BoF. Sequential tcPO2 values at baseline, immediately postfeed, and 10 minutes postfeed were significantly different for the feeding methods, with greater declines for BoF. Maximal temperature change, calculated by subtracting the baseline from the most extreme temperature for each feeding session, indicated that infants became significantly warmer during BrF than BoF. Although the small sample size necessitates replication, these results do not support the widely held assumption that BrF is more stressful than BoF for small preterm infants.