The ability of high-dose intravenous gammaglobulin (IVGG) to prevent the coronary artery lesion of Kawasaki disease has been studied in a multicentre controlled trial of IVGG plus aspirin versus aspirin alone, aspirin being the conventional treatment for Kawasaki disease. Patients were allocated at random to aspirin (45 cases) or IVGG (40 cases), there being no significant intergroup differences in age, sex ratio, duration of disease until the start of treatment, or severity. The development of coronary artery dilatation was monitored by two-dimensional echocardiography. Within 29 days of the onset of the disease, this lesion had developed in 19 cases (42%) in the aspirin group and in 6 cases (15%) in the IVGG group. There were no new instances of this lesion: in the period 30-60 days coronary artery dilatation persisted in 14 and 3 cases, respectively. In patients found to have echocardiographic abnormalities selective coronary arteriography was done 30-60 days after onset of Kawasaki disease and the lesion was confirmed in 1 of the 6 cases in the IVGG group and in 11 of the 19 controls. High-dose IVGG seems to reduce the frequency of coronary artery abnormalities in patients with Kawasaki disease.