Four groups of sero-negative cattle were brought into contact for various periods with either sero-positive and antigen-negative or sero- as well as antigen-positive animals. A seroconversion as evidence of transmission was only detected in animals that had been in contact with sero- and antigen-positive cattle. Shortest period of contact for those was 2 months after which a seroconversion was found. A distinct elevation of the number of lymphocytes was only detected in two animals which had been transported shortly after evidence of the seroconversion had occured.