Although the practice of using calf blood pressure (BP) measurement is widespread, virtually no information is available about calf site BP measurements in preterm infants. This research compared oscillometric upper arm BP measurements with calf BP measurements in 65 preterm infants with a mean weight of 1629 +/- 437 gm. Differences between arm and calf BP measurements were analyzed with repeated-measures multivariate analysis of variance of systolic, diastolic, and mean arterial pressures. There were no significant differences between arm and calf systolic BP on days 1, 3, and 5 of life. With post hoc testing there was a significant difference on day 7 between systolic arm BP (60.4 +/- 8.4 mm Hg) and calf BP (57.7 +/- 7.1 mm Hg) (t = 3.68, p < 0.01). There were no significant differences between arm and calf measurements for diastolic and mean arterial pressures and no main effect from infant weight on differences between arm and calf BP. It may be reasonable to use either arm or calf BP during the first 5 days of life.