The following article is a report of progress in a long term field study conducted by the University of California. The laboratories of the California Department of Agriculture cooperated with counsel and by making determinations of disease conditions during these trials. Farm Advisors W. F. Rooney, Tulare County, Ralph Pfost, Fresno County, W. W. Mitchell, Sacramento County, and Dr. M. A. Nilson, acting extension poultry pathologist, helped plan and conduct the trials.

The above progress report is based on Project No. 3966.

The strain of infectious bronchitis virus used for both challenge and inoculation and designated Massachusetts L-43 was obtained from Dr. Henry Van Roekel of the University of Massachusetts. Since October 1953 the virus used was prepared and donated for the trials by the Cutter Laboratories, Berkeley. Prior to that time the view was prepared in University of California laboratories at Davis.

The poultrymen in both areas and Drs. Ian McDonald. Jack Pflock, and S. F. Exstrom cooperated in the trials reported.