A method based on the intravenous 133Xe injection technique has been used for measurement of bone blood flow in man. The measurements were made from the greater trochanteric region of the femur of eight healthy subjects and three patients with bone marrow or a bone disease in which bone blood flow is known to be increased. The half-times of the fast and the slow compartments of the externally recorded two-exponential bone washout curves were 4.05 +/- 0.88 min and 45.4 +/- 7.4 min (mean +/- 1 sd) in the healthy subjects, 1.46 min and 20.1 min in the patient with chronic myeloid leukemia, 2.50 min and 22.9 min in metastic bone disease and 1.93 min and 18.1 min in the patient with osteosarcoma, respectively. The corresponding flow values were 11.5 +/- 1.4 ml/100 g/min (mean +/- 1 sd) in healthy subjects and 59.8, 28.3 and 34.0 ml/100 g/min in patients with bone disorders. The precision of the method estimated from the duplicate measurements in eight healthy persons is; for the fast compartment, 6.8%; and for the slow one, 3.2%. Because of the rapid washout of xenon and the very low radiation dose the measurements are easily repeatable.