The program under discussion is based on results obtained during transmission studies in which specific antibodies were detected in the immunodiffusion test earlier than antigen in peripheral blood leukocytes. Furthermore, it could be demonstrated that seroconversion does not seem to occur later than 3 months after transmission of the infectious agent. The results obtained in 11 herds are presented. The program is as follows: when the result of the immunodiffusion test becomes available all positive animals above 6 months of age are immediately removed from the herd. The remaining animals are checked at intervals of 3 months and sero-positives are always instantly removed. In pursuing the program a number of herds have obviously reachend 2 years old.