Buerger's colour. Cyanosis of the hands and feet in Buerger's disease is known as 'Buerger's colour'. This characteristic skin colour is produced by the subpapillary venous plexus. The reactions of the subpapillary venous plexus in patients with Buerger's disease were observed by analysing the fractional blood volume of tissue using a visible light reflective spectrophotometer. Capillary morphology was investigated using an intravital video-microscopic system. Twenty-seven subjects, comprising 13 normals and 14 patients with Buerger's disease, were studied. In the nailbeds of patients with Buerger's disease, an increase in the number of loops, cyanotic colour change and dilatation were observed. In this condition there was incompetence of venular tonus and regurgitation at venular valves. Buerger's colour is probably due to excessive congestion of venous blood in the subpapillary venous plexus which is produced by these mechanisms. 