PURPOSE: To determine the effects of pulmonary angiography performed with low-osmolar, nonionic contrast media on pulmonary artery pressures. PATIENTS AND METHODS: In a prospective, uncontrolled clinical trial, pulmonary artery pressures (systolic, diastolic, mean) of 116 patients referred for pulmonary angiography were recorded before and 1 and 5 minutes after injection of contrast material. RESULTS: There was a statistically significant rise in systolic, diastolic, and mean pulmonary artery pressure at 1 minute (4.6, 3.4, 4.1 mm Hg, respectively) and 5 minutes (3.8, 2.7, 3.4 mm Hg, respectively) after the initial contrast material injection (P < .05). Increases were smaller with additional injections. Systolic pressure changes at 1 and 5 minutes after the first injection were linearly dependent on the volume of contrast material injected (P < .05). There was no statistically significant difference in the increase in pulmonary artery pressure between patients with pulmonary embolus or pulmonary arterial hypertension and those without. CONCLUSION: There is a small but statistically significant rise in pulmonary artery pressure after injection of low-osmolar, nonionic contrast material for pulmonary angiography; it is unlikely to be of clinical significance.