Peripheral blood samples from 313 normal donors were tested for prior human cytomegalovirus (HCMV) infection: 37%, 0.9%, and 43% of the samples were positive by antibody detection, DNA hybridization, and RNA hybridization assays, respectively. An early mRNA, which is transcribed from a HindIII-b fragment of the CMV genome and detected with an antisense RNA probe, can be detected more frequently than antibody and CMV DNA. The early CMV mRNA transcripts can be detected in the peripheral white blood cells in 44% of HCMV-seronegative blood donors. Blood samples that were CMV RNA positive but antibody negative comprised 27% of the tested samples. Whether CMV RNA in donor blood indicates that CMV can be transmitted via blood transfusion must be determined by further studies.