Fatty aldehyde dimethyl acetals (DMA) derived from plasma and erythrocyte membrane plasmalogen phospholipids of 109 donors, aged 25-91 years, were measured as weight percent of total phospholipid fatty acids and DMA. The age range from 70 to 90 years (n = 82) was divided into age groups of five years each. Cumulative distributions of the DMA values of these age groups, when compared with those of 17 younger persons (aged 25-41 years), revealed a tendency to higher DMA values in the youngest age group, and to lower values in the oldest one. Linear regressions were computed between age and hexadecanaldimethylacetal (16:0 DMA) or octadecanaldimethylactal (18:0 DMA) of erythrocyte membrane and plasma phospholipids. Statistically significant negative correlations with age were obtained. Because of their sensitivity to oxidation reactions, a role of plasmalogens as a natural antioxidant in oxidative defense mechanisms appears to be convincing. However, it will possibly be difficult to separate the effects of normal aging on the decline of plasmalogen phospholipid levels in some tissues from those of certain pathological conditions - including hyperlipidemia and atherosclerosis.