Cardiovascular control was studied in five tetraplegic patients with physiologically complete cervical spinal cord transections. All had been injured less than two weeks previously and were in spinal shock. Blood pressure, heart rate, and plasma noradrenaline and adrenaline were measured at rest and during and after bladder stimulation and application of cold stimuli to skin below the level of the lesion. In three patients the cardiovascular responses to intravenously infused 1-noradrenaline and to the Valsalva manoeuvre were recorded. Measurements were also made in six chronic tetraplegic patients (in whom reflex spinal cord activity had returned) at rest, and during and after bladder stimulation, and in six normal subjects at rest. Average resting blood pressure in the recently injured tetraplegics was 130/57 (mean 81) mmHg, in the chronic tetraplegics 107/55 (mean 73) mmHg and in normal subjects 122/82 (mean 95) mmHg. Average resting heart rate was 64, 73 and 77 beats/min in the three groups respectively. Resting plasma noradrenaline and adrenaline levels in both the recently injured and chronic tetraplegics were lower than than in normal subjects. In the recently injured tetraplegics bladder stimulation caused minimal changes in blood pressure, heart rate and plasma noradrenaline and adrenaline levels. In the chronic tetraplegics similar stimulation caused marked hypertension, bradycardia and elevation in plasma noradrenaline but not adrenaline levels. Cold stimuli in the recently injured tetraplegics did not change blood pressure or heart rate. In the recently injured tetraplegics intravenous infusion of 1-noradrenaline resulted in greater elevation in blood pressure than normal. There was a decrease in heart rate. One patient was able to perform the Valsalva manoeuvre. His blood pressure responses were consistenly abnormal ('blocked' Valsalva).