The present invention provides an in-vivo intravascular blood replacing liquid which eliminates the need for the use of a contrast agent, is subjected to a low injection resistance, and has blood immunity to a sufficient degree and continuity to some extent. An in-vivo intravascular blood replacing liquid of the present invention is injected into a blood vessel to replace blood at an in-vivo intravascular portion to be inspected therewith in making an in-vivo intravascular inspection. The blood replacing liquid contains cationic and anionic compounds, added to an aqueous medium unharmful for the living body, which are unharmful for the living body. The blood replacing liquid also contains an ion complex formed of the cationic and anionic compounds.
