We isolated neutralizing human Fab fragment specific for human cytomegalovirus (HCMV) by phage display system. Fab libraries were constructed from peripheral lymphocyte of healthy individual. In several clones reacted for HCMV-infected HEL cells, one clone, designated 13-3, stained HCMV infected cells at 96 hrs post infection. It didn't react to cells at 6 hrs post infection or infected cells in the presence of AraC, meaning that 13-3 recognized protein synthesized at late times of infection. It also neutralized HCMV, Towne strain, efficiently. This neutralizing activity was specific for HCMV and no effect for HSV-1 and 2.