Presented paper deals with the relationship between immunoglobulin polyreactive properties and its lipid composition. Serum blood immunoglobulin fraction of an intact rabbit as an experimental model was used. Immunoglobulins (Ig) obtained by this way were transformed into polyreactive immunoglobulins (PRIg) by treatment with chaotropic agent KSCN or reactive oxygen species (ROS) with usage of Fe2+, EDTA and ascorbic acid. It was demonstrated that native Ig were able to bind with immobilized antigen (ovalbumin) and this ability dramatically increased after transformation of Ig into PRIg. The high immunoreactivity of PRIg was associated with marked fall (by 2-3 fold) of total phospholipids as well as individual ones--sphingomyelin and phosphatidylcholine. The main fatty acids of the Ig and PRIg phospholipid fractions in the sequence to decreasing decrease were stearic, palmitic, oleic and linoleic acids. The treatment of Ig by chaotropic agent and ROS led to decrease of stearic acid and enhancement of oleic, linoleic and arachidonic acids. The level of free cholesterol of Ig did not differ from that of PRIg. At the same time the content of cholesterol esters of PRIg was substantially diminished if compare with Ig. The main fatty acids of the Ig and PRIg cholesterol ester fraction in the sequence to decreasing were arachidonic, stearic, oleic, linoleic and palmitoleic acids. Transformation of Ig into PRIg was accompanied by enhancement of stearic acid level and loss of docosapentaenoic, arachidonic and palmitoleic acids. The results presented here support the idea about non peroxidative manner of the phospholipid and cholesterol ester extrusion from Ig molecule under its transformation into PRIg. Rather the last process could be explained by the term of concurrent physico-chemical interaction of Ig molecule with chaotropic agent or ROS leading to fall of lipid content. The presented data for the first time provide us an opportunity to conclude that transformation of Ig into PRIG is associated with the marked loss of essential phospholipids and cholesterol esters by the Ig molecule. The probable implication of this process in development of immune imbalance under certain diseases associated with oxidative stress have been discussed.