Controlled hypotension which is used during scoliosis surgery to improve operating conditions and minimize transfusion requirements may decrease spinal cord blood flow (SCBF). Previous studies using hydrogen washout, an invasive technique, have shown that trimethaphan-induced hypotension is associated with a decrease in SCBF, whereas hypotension induced with sodium nitroprusside or nitroglycerin is not. To determine whether the decrease seen with trimethaphan represented a generalized rather than regional spinal cord phenomenon, SCBF was measured at three separate cord levels (T2-3, 7-8, L2-3) using a noninvasive radionuclide-labelled microsphere technique. When the mean arterial pressure was reduced by 50%, SCBF decreased 35 to 45% at all levels of the cord examined, and remained at this reduced level during the period of hypotension. The results confirm that trimethaphan-induced hypotension is associated with a significant reduction in SCBF and that this occurs throughout the spinal cord during the period of hypotension.