Intraperitoneal injection is a common method of administering drugs or other substance to rodents. The injection site should be in the lower left or right quadrant of the abdomen because vital organs are absent from this area. In this protocol, we here present the experimental procedure of intraperitoneal injection in the mouse as follows. STEP 1
Draw the tail of the mouse from the cage and place it on the back of the hand for relax.
STEP 2
Manually restrain the mouse allowing abdomen side up and head end of mouse pointed down. Gently shake the mouse 2-3 times to encourage the intestinal content downward and to create an empty cavity in the lower abdominal quadrant, then swab the target site with 70% ethanol.
STEP 3
Quickly insert the needle into the inguinal area at a 45° angle. Penetrate gently just through abdominal wall (about 4-5mm). There will be an obvious resistance at the beginning of the puncture due to the tenacity of skin, and resistance will disappear as the needle has penetrated into the abdominal cavity. If foreign matter is drawn back into the syringe, then withdraw the needle and repeat the previous operation. If not, hold the syringe and insert the solution into the intraperitoneal cavity of the mouse.  
STEP 4
Withdraw the needle and rotate it slightly to prevent leakage. Finally, place the mouse back into the cage and continue feeding and observation.

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