Several carbonyls more toxic than malonaldehyde (MDA) are also generated during the propagation of lipid peroxidation stimulated "in vitro" in human erythrocytes. As regards thalassaemia, after "in vitro" treatment with tert-butyl hydroperoxide (TBHP), the total amount of aldehydes formed (MDA plus the other carbonyls) is significantly increased in the red cells from homozygous as compared to heterozygous and normal subjects. These findings lead to the conclusion that the extent of lipid peroxidation in erythrocytes is actually wider than that measurable in terms of malonaldehyde only, and that aldehydes of the hydroxyalkenal class in particular may play a role in the pathogenesis of reduced red cell survival in haemolytic anaemias.