Triosil 370 has been compared with Urografin 76, and Hypaque 65 by injecting identical volumes into the coronary arteries of human subjects in the course of coronary arteriography. The injection times used were the same and neither the patient nor the coronary artery catheter were moved between injections. The order in which the solutions compared were injected was alternated. The deviation in the ST segment and of the T wave which resulted from the injection was measured. The Triosil caused significantly less change than Urografin and Hypaque. A numerical expression of the T wave deflection derived from the data showed Triosil:Hypaque:Urografin equals I:2.6:2.9.