Diagnostically relevant polypeptides and fusion proteins comprising an amino acid sequence which originates from cytomegalovirus and corresponds to a region of the major DNA-binding protein or of the C-terminal region of the tegument protein pp150 fused with at least one further fragment from another antigenic protein of cytomegalovirus are disclosed. The major DNA-binding protein is encoded by the reading frame UL57. The poly-peptides and fusion proteins according to the invention can be used in an advantageous manner in diagnostic tests and methods for the detection of IgM antibodies against cytomegalovirus.