In Poland 35% of women, 25% of them being in reproductive age, smoke cigarettes. Substances included in tobacco smoke have highly toxic properties. Their presence in the human organizm may affect immunological mechanisms which are an important element determining dynamic balance betwen the mother and the fetus. The aim of the article is to compare the level of AFP and circulating immune complexes (KKI) concentrations in smoking and non smoking pregnant women in the second trimester. The levels of immunological complexes in the women's sera were determined by means of the Elisa immuno-enzymatic method using DRG Instruments GmbH Germany tests. The levels and the properties of circulating immune complexes were estimated in sera of 27 women being in the second trimester of pregnancy by means of polyethylene glycol (PEG) precipitation test. Molecular weight of the proteins of CIC was studied by SDS/PAGE. In the group of smoking women AFP levers were higher and KKI levels were lower than in the non smoking women group.