In 10 patients with a reflex urinary bladder after a cervical or high thoracic spinal cord injury, the effect of nifedipine on the cystometry-induced elevation of blood pressure was studied. The blood pressure was measured every 30 s in four consecutive cystometries before and after administration of 10 mg nifedipine sublingually. In each patient there was a decrease in the maximum systolic and diastolic blood pressure after the administration of nifedipine. In the whole group the mean maximum systolic pressure decreased significantly from 147 mmHg (range 119-165, SD 14) to 118 mmHg (range 99-145, SD 14). The mean maximum diastolic pressure decreased from 110 mmHg (range 96-124, SD 10) to 83 mmHg (range 71-99, SD 10). The effect of nifedipine was significant in each of the four cystometries that were performed. The decrease in blood pressure was due to both a significant decrease of the baseline pressure and a significant decrease of the blood pressure reaction during cystometry. Nifedipine may be useful in order to prevent dangerous blood pressure reactions, e.g. during cystoscopy and other diagnostic or therapeutic procedures in spinal cord injured patients with autonomic dysreflexia.