Adipose tissue blood flow in the forefoot was measured simultaneously with mean systemic arterial blood pressure over 24 hours in 8 patients (15 feet) with different degrees of arterial insufficiency. Mean systemic arterial pressure decreased by 19 ± 9% during sleep, irrespective of symptomatology. In two limbs, with a normal peripheral circulation, blood flow decreased by 8 ± 7%. In five limbs with arterial insufficiency, but no rest pain, blood flow decreased by 16 ± 8% and in eight limbs with ischaemic nocturnal rest pain blood flow was reduced by 32 ± 12% during sleep. It is concluded that nocturnal hypotension is a major factor in the production of nocturnal ischaemic rest pain.