IN RECENT years, there has been increasing interest in central venous pressure monitoring as a guide to fluid replacement in patients with problems of hypotension or hypovolemia. One of the problems barring such monitoring from wider usefulness in all patients, except the more seriously ill, has been the lack of ease in placing the catheter in the central veins. Peripheral venous pressure, which is relatively simple to measure, cannot be used to estimate changes in right atrial pressure with sufficient accuracy to be clinically helpful1; the only determination which is a reliable guide to circulatory dynamics is that made with a catheter lying in the right atrium, the vena caval system, or in an immediate tributary with no intervening valves.2,3 Many investigators make central venous pressure measurements by inserting a catheter, via a surgical cutdown on a branch of the brachial vein in the upper arm or on the