Acrolein is an alpha,beta-unsaturated aldehyde with enormous capacity of reaction, occurs in the air like a pollutant, but it is (we know now) an important lipid peroxidation product as well. The compound is one of the several aldehydes produced from fatty acid oxidation, although it is particularly important because it constitutes the major electrophyle aldehyde derived from lipid oxidation. Acrolein can be formed actively from oxidized fatty acids and undergo aldolic condensation in alkaline pH; this is a particular characteristic that we have used in its process of separation with capillary electrophoresis. We have shown that the oxidation of unsaturated fatty acids forms acrolein, and that the use of capillary electrophoresis to be a powerful, sensitive, and attractive method for separation, identification, and quantization of this and other aldehydes from in vitro lipid peroxidation.