We studied the damage caused to erythrocyte membranes by chlorophenoxyacetic herbicides. An increase in haemolysis was observed. The compounds investigated caused lipid bilayer damage by lipid peroxidation, as well as an increase in membrane fluidity at the 16th carbon atom of fatty acids was observed. Metabolites caused damage to membrane proteins - the free SH group content was increased. Higher toxicity of metabolites compared to basic compounds was observed.