In a double-blind randomized assignment of Renografin-76 or Hexabrix, 65 patients were evaluated to determine the safety and efficacy of Hexabrix, and to assess subtle differences and their implications in image quality. Dosage was adjusted for patient weight, and up to 150-ml of Hexabrix or Renografin-76 were injected over a 2-minute period during which rapid sequence CT was performed. Less heat and discomfort were noted with Hexabrix. No difference was evidenced in the side effects of emesis or hives, and no real difference in renal dysfunction was noted from a clinical standpoint. Image quality was generally equivalent, with possibly better renal concentration achieved with Hexabrix. © 1984 Lippincott-Raven Publishers.