Promotion is the exacerbation by certain esterase inhibitors (organophosphates, organophosphinates, sulfonyl halides, carbamates and thiocarbamates) of the clinical and morphological expression of toxic and traumatic axonopathies. Promotion is believed to interfere with mechanisms of compensation/repair of the nerves. The target of promotion is unknown but there are indications that it might be similar and/or linked to neuropathy target esterase (NTE), which is the molecular target of organophosphate-induced delayed polyneuropathy (OPIDP). OPIDP is the model axonopathy used to characterize promotion. NTE is defined as the activity resistant to paraoxon (40 microM) and sensitive to mipafox (50 microM). An esterase activity sensitive to higher concentrations (1 mM) of mipafox was identified in the nervous system homogenate, and its inhibition correlated with promotion. An activity with similar characteristics was present in the soluble fraction of peripheral nerves and could be physically separated (about 60 kDa). Identification and characterization of the target of promotion might be helpful in understanding the mechanism(s) of compensation and repair of the peripheral nervous system.