CMV specific IgM response is observed in latent reactivation, reinfection and sometimes during the course of non-CMV illness in addition to primary CMV infection. In the study, CMV IgG avidity test is evaluated in CMV IgM and IgG positive patients. Avidity index was below 40%in seven out of 39 patients (23.3%). In 22 patients that have CMV IgM positive results with at least two EIA systems, six (27.2) had low avidity index. On the other hand of 17 patients that have indeterminant CMV IgM result or reactivity at most one EIA system, one patient (5.9%) had low avidity index. CMV IgG avidity tests may be useful for diagnosis of primary CMV infection when used in coordination with CMV IgM and IgG EIA tests.