Foot temperatures of 36 patients were recorded continuously in the operating room and in the surgical intensive care unit (SICU) for 1-3 days. Operations included aortofemoral endarterectomy, arterioplasty, and bypass grafting. Regardless of severity of the operation, all had cold extremities on entering the SICU. The subsequent warming of the big toes, which started after 4-12 hours in the SICU, if at all, was classified according to a scheme of 6 deviations from a basic trend. This latter was a bilateral, continuous increase in 1-2 hours to 34 degrees C or higher where it remained with minor oscillations. Unilateral deviations were either diminished warming or no warming on one side. Bilateral deviations included stepwise increments to 34 degrees C, diminished increments, and no warming. Neurogenic vasospasm appeared to be the principal factor diminishing blood flow, with circulating vasoconstrictors and organic blocks as additional less important factors. Subsequent amputations of nine limbs were partially correlated with the categories of digital warming.