Immunoperoxidase technique has been applied to the rapid identification of human cytomegalovirus (CMV) strains on primary isolation. Negative and positive results have been constantly confirmed by indirect fluorescent antibody technique (IFA) and by electron microscopy. Using either direct or indirect method it was observed that problems of nonspecific staining of uninfected cells were encountered mostly with direct method, probably because of the lower working dilution of the conjugate (1:20) as compared with higher conjugate dilution used for indirect method (1:150). However, nonspecific cytoplasmic stain of Golgi area of infected cells was observed also with indirect method. Pathogenesis of nonspecific labelling of this area is discussed. Application of the immunoperoxidase technique directly into tubes on primary isolation allows to reduce identification time in comparison with IFA technique and is less cumbersome and time-consuming than complement fixation and neutralization tests.