This report described the infection of two strains of laboratory rats with a ratvirus (RA-1) with cytomegalovirus-like characteristics. The virus was detected in the spleens and kidneys during the first week post infection. In the salivary glands maximal virus titer was reached at one month post infection; thereafter the titer declined. In Lewis rats virus could be detected in the salivary homogenate of most animals at more than 12 months post infection. In BN rats, in contrast, virus became undetectable in the salivary glands of most animals 5 months after inoculation. However, administration of cyclophosphamide or X-irradiation resulted in reactivation of the virus in virtually all animals. Co-cultivation of spleen cells from either latently or chronically infected animals resulted in recovery of virus. The animals developed antibodies and a T-cell mediated virus specific cytotoxicity.