Polyunsaturated free fatty acids (PUFAs) participate in normal functioning of the cell, particularly in control intracellular cell signalling. As nutritional components they compose a human diet with an indirect promoting influence on tumourogenesis. The PUFAs level depends on the functional state of the membrane. This work is focused on changes only of free unsaturated fatty acids amount (AA - arachidonic acid, LA - linoleic acid, ALA - alpha-linolenic acid, palmitoleic acid (PA) and oleic acid) in cell membranes of colorectal cancer of pT3 stage, G2 grade without metastasis. Qualitative and quantitative composition of free unsaturated fatty acids in the membrane was determined by high-performance liquid chromatography. It was shown that the malignant transformation was accompanied by a decrease in amount of LA and ALA while arachidonic and oleic acids increased. It is of interest that free AA levels are elevated in colon cancer, as AA is the precursor to biologically active eicosanoids.