Blood-letting to a haematocrit of 0.40 to 0.42 was performed over a period of six weeks on 30 randomized patients with peripheral vascular disease (intermittent claudication), stage IIb (after Fontaine), in addition to standardized gymnastics and physical exercise (walking). Subsequently, 15 randomly selected patients received after each blood-letting middle-molecular hydroxyethyl starch solution, another 15 randomized patients received isotonic sodium chloride solution, both groups under a double-blind protocol, gymnastics and walking exercise being continued. At the beginning of the study both groups were comparable with respect to clinical and vascular parameters and results of laboratory tests. Those of the former group had a significantly greater increase in pain-free walking distance than the latter. Blood pressure levels remained unchanged in the former, but significantly rose in the latter. Peak flow during reactive hyperaemia increased significantly in both legs in the first group, remaining unchanged in the second. An increase in spontaneous platelet aggregation occurred only in the second group; alpha 2-macroglobulin concentration rose only in patients of the first group, while fibrinogen decreased significantly in both.