Universal use of low-osmolality contrast agents for intravascular diagnostic procedures has been limited to a large extent by the high cost of these agents, which is generally 10 to 20 times that of high-osmolality contrast media. The question for the radiologist, therefore, is the definition of selected populations and situations for the use of low-osmolality agents to achieve the greatest patient benefit at the least cost. The authors examine controversial issues including the incidence of significant contrast reactions, the definition and incidence of nephrotoxicity, and the effects of contrast media on coagulability.