A rate of malonic dialdehyde (MDA) degradation was studied in erythrocytes of newborns within the first and 4-5th days of life, of 5-6 and 8-14 years old children and of 18-28 and 35-49 years old adult persons by means of introduction of exogenous MDA into the mixture containing erythrocytes and estimation of the aldehyde elimination during incubation. Intensity of MDA degradation correlated with its content in erythrocytes. Age-, season- and circadian-dependent alterations were detected in the rate of MDA degradation as well as in the ratio of this value to the total content of MDA (index D/M). The lowest rate of MDA degradation and the index D/M value were observed in the persons of the older age group (35-49 years old). Either in 8-14 years old children or in adult persons the index D/M exhibited higher values in summer time as compared with other seasons. Distinct circadian alterations of the patterns studied were found in 18-28 years old persons but these patterns were dissimilarly directed during a day in newborns.