1. To localize the site of autonomic abnormality in patients undergoing haemodialysis, tests of overall autonomic function based on either changes in blood pressure (posture, sustained handgrip) or heart rate (Valsalva manoeuvre, 30:15 ratio, deep breathing test) were used. Integrity of the sympathetic efferent arc was examined by using the cold pressor test and the parasympathetic efferent arc by the atropine test. Eighteen patients and 12 control subjects were studied.

2. Changes in blood pressure on standing, sustained handgrip and in the cold pressor test were the same in the two groups.

3. In contrast, 11 patients had abnormal results in at least two of the three heart-rate-based tests.

4. Three of the 11 dialysis patients with evidence of autonomic involvement showed abnormal responses to atropine, indicating an efferent parasympathetic lesion, whereas the majority had a normal response to the atropine test, suggesting an afferent lesion only.

5. Evidence of autonomic involvement was not associated with hypertension nor confined to patients with dialysis hypotension.

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