In a prospective, controlled clinical trial, serial application of carbon-dioxide-enriched water was compared with fresh water. Twenty-four patients with peripheral arterial occlusive disease (stable claudication) were randomly allocated to one of two serial intervention groups, lower extremities immersed in either fresh water or in CO2-enriched water (1000 mg CO2/kg) water under standardized conditions (temperature, 33 degrees C; depth, 40 cm; immersion time, 30 min; five times a week over 4 weeks). The serial application of carbon-dioxide-enriched water increased arterial peak flow (reactive hyperemia), transcutaneous oxygen tension (basal value and half-recovery-time), and pain-free walking distance. The serial fresh water application did not change these values. The authors conclude that serial carbon dioxide application can be clinically effective in patients with arterial obstructions in the lower extremities.