The entire amino acid sequence of human cytomegalo-virus (HCMV) 150K matrix phosphoprotein (pp150), consisting of 1048 amino acid residues, was divided into 95 overlapping 20 amino acid peptides which were synthesized on polyethylene rods. The rods were subjected to ELISA with pooled anti-HCMV-positive and anti-HCMV-negative sera. Four peptides recognized by the anti-HCMV-positive pool only were synthesized by the solid-phase method and their reactivity in a conventional ELISA, using a panel of 14 individual anti-HCMV-negative and 20 anti-HCMV-positive antisera, was evaluated; three peptides were found to be specifically reactive. Results obtained with one of these peptides (residues 595 to 614) in ELISA showed a good correlation with those obtained using a routinely performed complement fixation test.