This study was designed to evaluate the gasometric and functional respiratory responses in chronic bronchitic patients with chronic respiratory insufficiency (CRI) under ambulatory oxygen therapy (AOT) with almitrine bismesylate (AB). It was a double-blind, placebo-controlled, randomized, prospective study which lasted three months and with a dosage regime of 50-100 mg/day of AB. Fiftyfour patients completed the study (28 in AB and 24 in the placebo (P) groups, respectively). All patients were males, with a mean age or 65 +/- 6.1 years. In the study of pulmonary function only airway resistance (Raw) was changed, with a significant decrease at the third month in the AB group compared with the P group (0.83 +/- 0.31 vs. 1.07 +/- 0.46 kpa/L.S), with a p value of 0.05 (mean +/- SD) and PaO2 which improved from 8.15 +/- 0.88 to 8.81 +/- 2.3 kpa (61.17 +/- 6.6 to 66.10 +/- 10 mmHg), with a p value of 0.05. AB therapy was well tolerated.