The concept of an electromagnetic flowmeter was first described by Kolin in 1936. He demonstrated that with the flowmeter which required surgical exposure of the blood vessel for probe contact but not requiring cannulation, it was possible to follow rapid flow changes and that the deflection bore a linear relationship to flow. Twenty years later a greatly improved circuitry and design was described by Denison and Spencer. Soon thereafter, a number of investigators, notably Schenk and his colleagues utilizing the square wave electromagnetic flowmeter and Cannon and his colleagues with the sine wave electromagnetic flowmeter reported on a number of experimental and clinical studies on blood flow measurements. My introduction to blood flow measurements was through Ferguson who had had a flowmeter and flowmeter probes constructed according to the design of Denison and Spencer. Our first report on flow measurements in patients with peripheral arterial disease was made in 1960. Electromagnetic flowmeters and probes available today are a vast improvement in ease of use, reliability and accuracy, thus the pertinent question is whether or not the information that can be obtained with it would warrant its routine clinical use. We started with a flowmeter constructed by following a schematic diagram and hand winding our own probes, then to the purchase of Medicon 2000, then Medicon 4000, and to our present unit, the SP2204. The advancement in instrumentation has been truly remarkable. All intraoperative blood pressure measurements are made with direct arterial puncture with 23 size needle with the hub removed and needle tip fitted to polyethylene tube connected to a strain gauge.(ABSTRACT TRUNCATED AT 250 WORDS)