The uteroplacental circulation in the placenta can have a major impact on the fetus. Near infrared spectroscopy (NIRS) is the noninvasive method of measuring changes in blood volumes and oxygen concentrations in living tissue. The purpose of this study is to monitor changes in placental tissue oxygen index (TOI) levels, in patients with intrauterine fetal growth restriction during pregnancy, using NIRS. We measured placental TOI values of 15 normal pregnant woman and 15 patients with intrauterine growth restriction admitted to our hospital. The placenta was assessed by ultrasound examination and NIRS was performed on all patients. The TOI values of the IUGR group when hospitalized was 78.6 +/- 1.6 (SD). This value was significantly higher than that of the controls (78.6 +/- 1.6 [SD] versus 70.2 +/- 0.4 [SD]). And the TOI values of the IUGR group, when measured before delivery, were 77.8 +/- 1.6 (SD). The TOI values of the IUGR group before delivery were significantly higher than those of the control group (77.8 +/- 1.6 [SD] versus 70.3 +/- 0.4 [SD]). We propose that NIRS is a candidate, noninvasive method for assessing placental oxygen dynamics on a real-time basis. In the near future it may contribute to perinatal medical practice.