Serum albumin fatty acid composition of patients with lung and mammary gland oncopathology was investigated by chromatography method. Differences in the contents of families 6 and 3 fatty acids were showed that depend on disease stage and tumour localization. omega 6/ omega 3 ratio increase in the early stages of tumour process was established for both pathologies. These findings can be used in a diagnostic test to discover early stages of tumour.