To elucidate correlation between processes of lipid peroxidation (LP) and accumulation of peptides from the group of "middle molecules" (PMM) in blood, we made investigation of blood of 81 patients with ischemic and hemorrhagic stroke. Gel-filtration column chromatography for PMM separation was performed. Divided fractions were registered with UV-monitor at wave length equal to 254 nm. The character of both spontaneous and Fe(2+)-induced chemiluminescence, the level of malonic dialdehyde (MDA) and conjugated dienes (CD) were estimated. It was established that the level of LP processes was significantly increased in blood and erythrocytes of patients with stroke, especially in hemorrhagic form. The total content of PMM, especially of A and A4 fractions, as well as D and F fractions was almost twice as much in blood. A correlation was observed between accumulation of PMM in blood of patients with stroke and PL induction, that may be the factor of PMM generation. A conclusion was made, that accumulation of some PMM classes in blood of patients with strokes was related to LP processes, which were responsible for the severity of the secondary pathochemical alterations in tissues of the brain. These findings should be considered in elaboration of drug treatment and estimation of the disease prognosis.