The results were analysed of 485 (biplane) cineangiocardiograms performed in 200 consecutive cardiac investigations on neonates (under 4 wk) and infants (4 wk to 1 yr). 10 deaths occurred during or within 24 h of cardiac catheterization, all in patients who were profoundly acidemic because of their hemodynamic disturbance. A total dose of Cardio-Conray at any one investigation of 4-5 ml/kg body weight was satisfactory and without undue risk. Single injections of 1.5-2.0 ml/kg body weight were safe whilst providing optimal diagnostic information. The interval between multiple injections did not appear to affect the risk to the patients.