Two consecutive measurements of resting CBF were carried out in normal volunteers (n = 25) using H2(15)O positron emission tomography. Absolute whole-brain blood flow (WBBF; ml 100 g-1 min-1, mean +/- SD) for the first (40.3 +/- 6.4) and second (39.3 +/- 6.5) measurements was not significantly different (mean % difference 2.3 +/- 8.7). Analysis of regions of interest showed no significant differences in absolute regional CBF (rCBF) and normalized (rCBF/WBBF) rCBF. Left-right differences were also not significant. These data demonstrate the reproducibility of resting CBF measurements in normal humans.