Maternal serum samples at 10 and 22 weeks of gestational age and cord blood samples were available from six cases of asymptomatic congenital human cytomegalovirus (HCMV) infection. Meaningful rises of serum IgG-antibody titers by ELISA occurred in three cases. Serum interferon (IFN)-gamma activity was detected in all six cases. Serum cell free soluble interleukin-2 receptor (sIL-2R) activity rose above the normal range (145-519 U/ml) in one IgG and IgM antibody-positive and three IgG antibody-positive woman. Serum levels of sIL-2R and IFN-gamma were not elevated in anti-HCMV antibody-negative healthy pregnant women. No HCMV IE DNA was detected by PCR in the serum of any of the pregnant women. HCMV DNA was detected in the serum of one of six infants with asymptomatic congenital HCMV infection. Assessment of the changes of serum cytokines such as sIL-2R and IFN-gamma in HCMV antibody-positive pregnant women may be useful for the prenatal diagnosis of active HCMV infection during pregnancy.