Exposure to chronic hypoxia results in hypoxic pulmonary hypertension (HPH) characterized by remodeling of peripheral pulmonary vasculature. Collagenolytic enzymes produced by hypoxia-activated mast cells may play an important role. Present study determines whether disodium cromoglycate (DSCG) an inhibitor of the mast cell secretion prevents HPH in rats exposed to chronic hypoxia. Four groups of adult male Wistar rats were studied. Experimental groups were exposed for 3 weeks to isobaric hypoxia (FIO2 0.1) and treated with DSCG (40 mg/kg, i.p.). DSCG was given first 4 days of hypoxic exposure (group DSCG + H, n = 8) and last 4 days of exposure (H + DSCG, n = 8). These groups were compared with untreated rats exposed to hypoxia (H, n = 8) and with normoxic controls (C, n = 8). Pulmonary arterial blood pressure (PAP) was significantly increased in all hypoxic groups. PAP was significantly lower in group DSCG + H (25 ± 2 mmHg, P< 0,05) than in groups H (30 ± 2 mmHg) and H + DSCG (33 ± 2 mmHg). We conclude that DSCG applied in the early phase of exposure to hypoxia significantly reduces the development of HPH. The mast cells degranulation seems to be an important factor in pulmonary vascular remodeling. Supported by GACR 305/05/0672 and 1M6798582302.