An ELISA method using human CMV major polypeptide (66 kD) purified by electroelution was used to detect IgG and IgM antibodies and was compared with a conventional ELISA using the whole virus. The ELISA-66 kD showed a good sensitivity (98.2%) and had a better specificity than the ELISA-whole virus (97.5% versus 80.3%). Cross reactions observed, particularly with sera containing anti-EBV antibodies, were ruled out.