A practical procedure for hypophysectomy of the mouse by paraphyaryngeal approach has been developed by modifying the technics of Motizuki [5] and Lostroh and Jordan [4]. Postoperative care in C3H/He strain of female mice was also studied. The main points improved are as follows: (a) The dental drill bar made of a needle with 2mm outer diameter was devised for making a hole in the cranium (Fig. 2). The bar does not grind the cranium, but cuts it in the circle, resulting in speeding up of the operation and in little bleeding, since the hole is very small. (b) Special attention was paid in breathing of mice during the operation. A longitudinal midline incision of about 1cm was made in muscle encircled the trachea and a pinhole was made by sewing needle into the trachea. A small piece of cotton wool was put on the pinhole and covered by the muscle. It admirably keeps the tracheal hole open for breathing during operation (Fig. 1). (c) After the operation, the mouse was placed in a chamber filled with an atmosphere of 95% O2-5%CO2 gas until recovered, otherwise, all mice died in a few days after operation with inflamation of the lung. The temperature of the recovery chamber is recommended to be kept at about 28 degrees C for ensuring the resuscitation. The intraperitoneal injections of hydrocortone-acetate (0.25mg/0.1ml) just before and 2 days after operation further ameriolated the survival rate.