Previous hypotheses about the causes of venous ulceration are inconsistent with recently published data. In patients with chronic venous insufficiency the number of functioning capillary loops visible in the skin on microscopy fell after the legs had been dependent for 30 minutes. Another study had shown that leucocytes became trapped in the circulation in dependent legs. A new hypothesis linking these two findings proposes that the trapped while cells occlude the capillaries and result in ischaemia of the skin of the leg.