In a series of 65 patients with a variety of conditions, velocity of blood flow was measured by determinations of arm-to-ear, right atrium-to-ear, pulmonary artery-to-ear, and pulmonary capillaries-to-ear circulation times. The arm-to-ear time, representing an equivalent of the bedside "circulation time test," and the blood velocity through the various intermediate segments were correlated with cardiac output, right atrial pressure, and left atrial pressure. There is a broad, but definite relationship between circulation time and some of its component time measurements, on the one hand, and cardiac output, on the other hand. However, no relationship was found between atrial pressure increases —as indices of failure of the cardiac ventricles— and circulation time. The clinical use of "circulation time" is considered to be of very little practical value.