Taking advantage of the exposure of dural sinuses during craniotomies, we measured confluens sinuum pressure by direct catheterization. The influence of various surgical positions and of other factors on confluens sinuum pressure was studied. When the upper half of the body was raised, the confluens sinuum pressure decreased to reach zero at +25 degrees; when the angle was +90 degrees, a marked negative pressure of -12.7 +/- 3.0 cm H2O (mean +/- SD) was observed in adults. In children under 6 years of age, however, such negative pressure was not observed even at an angle of +90 degrees. The confluens sinuum pressure was 2.7 +/- 0.6 cm H2O with the patient in the reverse jackknife position (supine position with the upper and lower halves of the body elevated ca. 20 degrees), 3.0 +/- 0.8 in the sea lion position (prone position with the upper and lower halves of the body elevated ca. 20 degrees and with the neck hyperextended), 5.8 +/- 0.9 in the prone position, and 5.9 +/- 1.7 in the supine position. In the supine and the sitting positions, the confluens sinuum pressure was elevated well enough by jugular compression to prevent air embolism. Positive pressure respiration did not raise the confluens sinuum pressure. The pressure of the jugular bulb measured by percutaneous direct puncture did not always reflect the confluens sinuum pressure, probably because subcutaneous hematoma produced an effect similar to that of jugular compression.