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Tim NATtrm~ of functional changes occurring in chronic quadraplegic patients and the mechanisms responsible for the altered responses ~o stress situations, which occur in these patients, are not yet clearly defined and understood. Anaesthesia and surgery are examples of stress situations in which these patients respond in abnormal fashion, and instability of the circulation during surgery has been of concern to anaesthetists. 1-4. These patients often experience precipitous falls in blood pressure as a response to exceedingly small doses of anaesthetic agents. We have investigated the total blood volume and the compliance of the capacitance vessels of the circulation in the upper limb in a group of such patients, in an endeavour to define some of the altered responses in the chronic quadraplegic, which might account for this troublesome fall in blood pressure and which might point the way to some measures of control to improve the risk of anaesthesia and operation in these patients. ~ METHOD AND MATEI~IALS A group of 27 quadraplegic patients was chosen at random for this study. Blood volumes were measured in all cases using I TM albumen (RISA) and the "Volumetron".| The calculation was based on the weight of the patient at the time of the current admission to hospital. Again on a random selection basis, seven patients had upper limb plethysmography. Capacitance vessel compliance of the forearm was determined with a Whitney mercury-in-rubber gauge. Normal vessel compliance was first recorded. A mild stress was then applied, through the use of a Bird respirator set in the assist/control position, and triggered by the patient. G,s A positive pressure sufficient to cause alteration in venous return was added, and again the limb vessel compliance was recorded. No changes in compliance could be recorded in any of the patients studied. The anaesthetist who haphazardly injects a large dose of thiopentone into this type of patient during induction might be doing him a great disservice, by dilating a resistance and capacitance system which has no means of retaliating against this aggression. We have observed many times under such conditions that blood pressures which start at normal levels may soon fall to levels at which cerebral, coronary and renal function cannot be maintained.