Efficacy and safety of almitrine bismesylate was assessed in COPD patients in a 6 month open prospective multicentre trial. The study enrolled 598 COPD patients with moderate hypoxemia (males / females, 484 / 114, mean age, 60.7 ± 9.3 yrs; mean FEV1, 46.1 ± 16.4 % pred, mean PaO2, 55.7 ± 16.4 mmHg, mean SpO2, 88.4 ± 4.7 %). We used an intermittent regime of almitrine administration: 1 mg / kg / day for 3 months, then a 1 month "window" and then active 2 month therapy again. Almitrine therapy resulted in improvement of dyspnea on daily life activity (MRC score): from 3.5 ± 0.8 to 3.0 ± 0.8 (in 1 month), 2.5 ± 0.8 (in 3 months), 2.5 ± 0.7 (in 6 months) (р < 0.001). There was a significant increase in РаО2: a rise to 59.9 ± 16.1 mmHg in 1 month, to 60.8 ± 15.9 mmHg in 3 months and to 61.5 ± 14.0 mmHg in 6 months (р < 0.001). The 6 minute walk distance increased from 290 ± 118 m to 328 ± 128 m in 3 months and to 333 ± 145 m in 6 months (р < 0.001). Eighty three (13.9 %) patients dropped out of the study for various reasons. The most common adverse effects were gastro intestinal disorders (4.7 %) and peripheral polyneuropathy (3.8 %). Conclusions: almitrine administration in COPD patients with moderate hypoxemia resulted in reducing dyspnea on daily life activity, increase in physical capacity, improvement of arterial oxygenation. Almitrine therapy was well tolerated by most the patients.