All current intravascular radiological contrast media are salts and produce solutions of very high osmolality--five to eight times that or tissue cells, plasma or tissue fluid (all of which have an osmolality of 300 mosmols per kg water). Erythrocytes and vascular endothelium are adversely affected by the high osmolality of intravascular contrast media, resulting in tissue anoxia and increased capillary permeability, the latter causing damage to the blood-brain barrier. Vasodilatation, systemic hypotension and osmotic hypervolaemia are generalized manifestations of the high osmolality of contrast media. New low osmolality contrast media have been synthesized, utilizing a non-ionizing radical (such as amide or amine) instead of the carboxyl group of a tri-iodinated substituted benzoic acid. Such examples are metrizamide (Amipaque) and Iopamidol (both non-ionic amides) and Hexabrix (salts of a mono-acid dimer). Early clinical evaluation suggests that these low osmolality solutions have major advantages in reducing pain, heat sensation and adverse reactions of angiography.