Recurrent miscarriage occurs in 1 - 5 % of women at reproductive age. The most common cause of recurrent miscarriage is chromosomal abnormalities of the embryo (41%), chromosomal aberrations parents (10%), anatomical abnormalities of the uterus (5%), infectious and hormonal factors. In about 25% of women, no cause of recurrent miscarriage is usually found. Therefore it seems important to study all factors possibly inducing pregnancy disorders. Objective: The aim of this study was to find a difference in serum protein fractions between women with primary and secondary recurrent miscarriage. Methods: The study group consisted of 52 women (aged 36.0±4.9) with recurrent miscarriage. Nine of them (17%) reported one earlier regular pregnancy ending with childbirth without complications. Control group comprised 30 non-pregnant women (aged 36.1±3.6), who had given vaginal birth to healthy children at least twice. Serum protein fractions were separated by electrophoresis in the SDS PAGE buffer system using a Mini PROTEAN 3 cell device. BioRad SDS PAGE Molecular Weight Standards covering mass range of 6.5-200 kDa were used as a reference. Gels were stained with Coomassie Blue R 250 solution. BioRad QuantityOne software was used for the assessment of molecular weight of each protein fraction. Results: Electrophoretic separation revealed 39 protein fractions of 10 243 kDa. Particularly interesting was a 38 kDa fraction present exclusively in serum of women with recurrent pregnancy, who had never given birth. Another fraction (74 kDa), not detected in the control group, was found in all women with recurrent pregnancy loss. Protein fractions of 76 and 151 kDa were present only in the control group. Conclusions: The presence of the protein fractions of low- or mid-weight in serum from women with recurrent miscarriage may potentially play a role in the pathomechanism of this disorder.