Temporal vein injection is a technique used to deliver substances systemically via the superficial temporal vein, commonly in neonatal rodents. The protocol involves warming the subject to dilate veins, restraining gently, identifying the temporal vein, cleaning the site with an antiseptic, inserting a fine-gauge needle at a shallow angle, slowly injecting the substance, and monitoring post-injection recovery. This method is often used in pharmacokinetics, gene therapy, and neonatal studies.