Dopamine (DA) has rarely been administered at low dosage to stable patients with pulmonary hypertension (PAH) secondary to chronic obstructive lung disease (COLD). Since L-dopa (L-DA) is metabolized into DA, it might be an oral source of DA. After informed consent 10 patients with PAH, secondary to COLD underwent right catheterization to allow measurements of pressures and cardiac output (CO) as well as arterial and mixed venous oxygen levels before and then 30 and 60 min after the beginning of intravenous DA at a rate of 4 micrograms/kg/min. A week later, the same parameters were remeasured in 5 of these patients after a single oral intake of 1.5 g L-DA. At low doses both DA and L-DA increased CO and decreased pulmonary vascular resistances, suggesting a pulmonary vasodilator effect. They also enhanced oxygen delivery and Pvo2 without decreasing Pao2. A correlation was observed between cardiac index and plasma DA level. Thus though they do have some immediate adverse side effects and their long-term effects are unknown, inotropic and vasodilator drugs may have positive effects on pulmonary circulation.