The possibility of elastase contributing to degradation of the arterial wall in atherosclerosis and to the formation of ectasia has prompted us to assay the main protease inhibitors, alpha 1-antitrypsin and alpha 2-macroglobulin, in patients with angiographic coronary disease with and without coronary ectasia. Serum concentrations of these two proteins were measured by immunonephelometry in 203 patients admitted for coronary arteriography. The results obtained were analyzed according to the presence of atheromatous lesions and their severity and to the presence or absence of ectasia. There was no correlation between the values observed and the presence or severity of coronary atherosclerosis, but the concentration of alpha 1-antitrypsin was significantly higher in patients with coronary ectasia (247.2 +/- 40.5 mg/ml) than in patients without ectasia (213.5 +/- 36.6 mg/100 ml; p less than 0.001). This study shows that coronary ectasia is associated with disturbances in the protease-antiprotease system, which may be consecutive to initial changes in elastase activity. Our results support the theory that elastase and protease inhibitors play a specific role in some atheromatous processes.