The haemodynamic side-effects of ionic (amidotrizoate) and non-ionic (iopamidol) contrast media after injection into the right atrium were compared in experimental and clinical studies. Pulmonary hypertension was induced in 10 dogs by embolization of the pulmonary vascular bed with agar-agar solution (mean pulmonary artery pressure = 44.2 mmHg). Iopamidol (1.5 ml kg-1) caused a moderate decrease in pulmonary and systemic vascular resistance, slight increases in right ventricular end-diastolic pressure and a marked rise in right ventricular contractility (dP/dtmax). Amidotrizoate (1.5 ml kg-1) caused considerable systemic vasodilation and initial increases in pulmonary vascular resistance and pressure followed by a substantial increase in right ventricular end-diastolic pressure and a decrease in contractility. Central and peripheral haemodynamics were measured in 20 patients with pulmonary hypertension (mean pulmonary artery pressure = 38.1 mmHg) due to valvular heart disease before and following injections with 40 ml of both types of contrast medium in randomized order. Heart rate, cardiac output and right atrial pressure rose significantly more after amidotrizoate and this contrast medium caused more extensive systemic vasodilation and a larger decrease in aortic pressure as compared to iopamidol. Pulmonary artery pressure went up moderately with both contrast media. It is concluded that non-ionic low-osmolality contrast media like iopamidol induce less pronounced haemodynamic alterations, in particular less increase in right ventricular filling pressure. This may be beneficial to patients with pulmonary hypertension undergoing angiocardiography or digital subtraction angiography.