Immunoblot analysis using mouse monoclonal antibody to human IgM detected IgM to cytomegalovirus (CMV)- specific proteins (150, 42, 38, 32, and 28 kDa) in 74 (38 %) of 197 seropositive serum samples from 197 individuals in three subject groups: 43 surgical patients, 31 patients with solid tumors, and 123 healthy individuals.