2,4-dichlorophenoxyacetic acid (2,4-D) is a herbicide commonly used in agriculture. The residues of 2,4-D are present in air, water, soil and edibles. It constitutes a real hazard for human and animal health as numerous accidents of poisoning deaths caused by this herbicide have been reported. However, the molecular mechanism of its action is still unknown. The point of view concerning the toxic action of 2,4-dichloro-phenoxyacetic acid has been evolving from decades and now it is considered that 2,4-D also induces free radical reactions that lead to numerous unbeneficial changes in tissues. The increases of free radical levels cause DNA damage and thus cell death (in apoptotic process). It is also suggested that 2,4-D causes cell apoptosis as the result of change of membrane potential in mitochondria and initiates caspase-dependent reactions. For many years the discussion has been continuing concerning the mutagenicity of 2,4-D and now many documented investigations that have been performed from 2000 unequivocally proved its mutagenic action. The mutagenicity of 2,4-D concerns homologous recombination, A→G mutation, chromosome aberrations, sister chromatid exchange and DNA damage, and also an increase in the frequency of DNA strand breaks. This paper presents literature data (especially the newest that have been published since 2000) that refer to peroxidative capacity of 2,4-D, free radical formation, induction of apoptosis, genotoxic activity and adaptation of the cells and organisms to its action.