Summary.4‐Aniino‐3,5,6‐trichloropicolinic acid was incubated at 70° F in thirteen different soils for periods of up to 2 years at a concentration range of 0–023–24 ppm. Losses varied from complete to non‐measurable by the bioassay technique employed. The percentage decomposed was generally greater for lower initial concentrations. The results were mathematically analysed in terms of zero‐order, half‐order, first‐order and Michaclis‐Menten kinetics. Half‐order and Mirhaelis‐Menten were found to be the kinetic expressions that most satisfactorily described the detoxification of the herbicide in soil.Taux de deloxification de l'acide 4‐amino‐3,5,6‐t