SUMMARYThe RNA content of four different CMV strains was investigated. All RNA preparations always contained the four major RNA species described by Kaper & West (I972), while most preparations also contained several minor RNA species. The four largest RNAs were separated by sucrose density-gradient centrifuging and by electrophoresis on polyacrylamide gels. Combination experiments suggest, for all strains, that the genome consists of the three largest RNAs (1 + 2 + 3), while RNA 4 is not required for infectivity.The distribution of RNAs in the capsids could not be established unequivocally, and the situation possibly differs in different strains.