Using ozonization and thin-layer chromatographic methods we determined the qualitative and quantitative correlation of unsaturation distribution (UD) in individual fractions of blood plasma lipids in children suffering from insulin-dependent diabetes mellitus (IDDM). The research was aimed at elucidation of biochemical criterion of the degree of metabolic disorders in children with IDDM and at development of methods for quantitative assessment of such disorders. Twenty children were examined during the compensation stage (group 1), and twelve during decompensation with ketoacidosis (group 2). The present investigation shows that in the case of insulin-dependent diabetes mellitus in children the total unsaturation distribution (TUD) in plasma lipid fractions were found to be decreased significantly compared to healthy controls. The pattern of TUD in plasma lipid fractions may serve as a new biochemical criterion for metabolic disorders and decompensation in IDDM.