With the development of low osmolar and nonionic contrast media in clinical practice, radiologists have enjoyed increased clinical application along with other advantages such as improvement of patient comfort and safety. Recently, radiologists have introduced many intravascular pharmacologic agents to improve diagnostic quality and patient safety. Shortly after the introduction of these agents, however, it was observed that a precipitate results when a certain pharmacologic agent is mixed with a low osmolar contrast media. These observations have prompted testing of several other drugs used for incompatability with contrast media. To verify these reports and to investigate other medications not previously tested, the authors analyzed mixtures of contrast agents and medications in vitro and observed them for visible precipitates after operating the highspeed centrifuge. The results were as follows: 1.The contrast media that produced incompatibilities with some pharmacologic agents were ioxaglate, diatrizote, and iothalamate in the order of frequency. 2.The contrast media that produced no precipitate were iopromide and ioxithalamate. 3. The pharmacologic agents that produced precipitate with some contrast media were papaverine, Benadry 1, Protamine, Cimetidine, Regitin, and Gentamicin. Therefore, we recommend that caution should be taken to recognize incompatibilities and avoid them when intravascular pharmacologic agents of any kind may be incompatible.