The aim of this study was to assess oxidative stress in pregnant women infected with cytomegalovirus on the basis of 3-nitrotyrosine levels in amniotic fluid (AF). The 3-nitrotyrosine (3-NT) level in AF was measured using the competitive ELISA method. The study groups were as follows: group I consisted of women with IgM and/or IgA; group II were women with only IgG anti-CMV antibodies and group III were seronegative women, used as the control group. Age, gestational age and socioeconomic status were also assessed. The average level of 3-nitrotyrosine in group II and the control group was similar: 53.14 nM 3-NT and 49.78 nM 3-NT, respectively. However, in group I, the lowest level 3-NT in AF was observed - 39.17 nM 3-NT and statistical analysis showed significant differences in levels of 3-NT between group I and the control group (p < 0.01). We conclude that significantly lower levels of 3-nitrotyrosine in pregnant women with CMV infection may indicate an increase in the antioxidant defence mechanisms in these patients.