The chronic respiratory disease virus (CRD) used in this study was obtained from Dr. James E. Porter of the Salisbury branch of the Live Stock Sanitary Service and was strain #26539 which was a pool from the sinus and hock of 4 chickens from a flock of 15,000 infected birds.Laryngotracheitis virus used was designated as #27143 and was the exudate from the trachea of infected chickens which had been used as a vaccine and inoculum for reinfection of other birds.Dr. T. O. Roby of the Pathological Division, Bureau of Animal Industry, Agriculture Research Administration, Washington, D. C., supplied the swamp fever virus in the form of infected horse serum #1531. This serum was proved to contain the New Hampshire strain of swamp fever virus.This experiment was carried out to determine the susceptibility of the Swiss albino mouse to the 3 viruses by various routes of exposure.MATERIALS AND METHODS …