Regional cerebral blood flow (rCBF) was measured in patients with no neurological deficit and no abnormal findings of cerebral angiograms except aneurysm itself with Xenon-133 injection technique by using the computerized 32-detector rCBF system (rCBF-322, Meditronic, Denmark). This system consists of a 32-detector head with a concave surface and a 32 pulse height analyser and analog-digital ratemeter as the accumulator connected to display units with an oscilloscope for 32 clearance curves and also a microcomputer programmed for calculating the rCBF initial with the initial slope analysis, for calculating the rCBF 10 with the height-over-area method and the rCBF gray, rCBF white, weight gray and weight white with the SHAM method. The results obtained were as follows: 1) The mean value and SD of rCBF initial was 58.4 +/- 6.2 ml/100 g brain/min; rCBF 10, 50.6 +/- 5.0 ml/100 g brain/min; rCBF gray, 78.0 +/- 14.0 ml/100 g brain/min; rCBF white, 22.1 +/- 6.6 ml/100 g brain/min; weight gray, 49.0 +/- 3.7%; weight white, 51.0 +/- 3.7%. These data should be considered normal values as reported also by others. 2) Reproducibilities were estimated by measuring twice the rCBF initial and the rCBF 10 at rest with closed eyes. The reproducibilities of the rCBF initial eyes 13.55% (P less than 0.05) and one of the rCBF 10 was 8.85% (P less than 0.05). It was concluded that this system should be widely used for measuring the rCBF in patients with various cerebral diseases.