A meta-analysis of the effects of nonnutritive sucking (NNS) on heart rate and transcutaneous oxygen tension (TcPaO2) was performed. Four studies of NNS on heart rate without stimulations, three studies on heart rate during painful stimulations, and three studies on TcPaO2--all conducted over the past 30 years--were found through a computer search. Using the Fisher combined test, NNS significantly decreased heart rate without stimulations (p = .002) and during painful stimulations (p = .0001), and significantly increased TcPaO2 (p = .0001). The total weighted effect size for heart rate without stimulations was small (0.17); however, it was large for heart rate during painful stimulations (1.05) and TcPaO2 (0.69). Larger effects were noticed for preterm infants than for term infants and for longer NNS. More studies of NNS effects with independent treatment and control groups, using the physiological outcome variables of heart rate and oxygenation for different age groups of preterm infants, are needed to examine the fundamental mechanisms of NNS effects. Clinically, a low-risk intervention such as NNS can be more broadly used during any painful procedures to decrease infant distress.