The water soluble contrast media cause tissue necrosis infrequentely by extravasation during intravenous injection in various radiological examinations. However it has not been well documented that what kind and what concentration of contrast media can cause tissue necrosis. And also the mechanism of tissue necrosis by extravasated contrast media has not been well known. The purpose of this experimental study was to evaluate the frequency and severity of tissue damage following subcutaneous injection of various water soluble contrast media to investi-gate the characteristics of the contrast media acting on the tissue damage and to provide the basic data for the clinical application, Meglumine ioxithalamate sodium and meglumine ioxithalamate iopromide iopamidol iox-aglate meglumine diatrizoate and sodium diatrizoate of various iodine content and osmolality were injected into subcutaneous tissue of the dorsum of 970 feet of 485 rats. The tissue reaction of injection sites were grossly examined with period from 1 day to 8 weeks after the injection, Representative gross changes were correlated with histologic findings. The results were as follows; 1. The basic tissue damage by extravasated contrast media was acute and chronic inflammatory reaction of the soft tissue with subsequent progress into the henmorrhagic and necrotizing lesion, 2. Larger volume of contrast media cause more severe tissue damage. 3. Contrast media of higher osmolality caused more severe tissue damage. 4. AT same osmolality contrast media of higher iodine content caused more severe tissue damage.5. Ionic contrast media of meglumine salt caused more severe tissue damage than those of sodium salt. 6. There was no significant difference of tissue damage between ionic and non-ionic contrast media under the same or similar osmolality and iodine content. 7. The younger rats showed more severe tissue damage by contrast media of high osmolality. It is therefore recommended to use the contrast media of lower osmolality and lower iodine content regardless of ionic or non-ionic and to use the contrast media containing sodium salt rather than meglumine salt in case of high risk of extravasation in clinical practice.