Abstract: We studied the expression of acetylcholinesterase (AChE) in the nervous system (cerebellum, optic lobes, and neuroretina) of the quail at different stages of development, from embryonic day 10 (E10) to the adult. Analyzing AChE mRNAs and AChE molecular forms, we observed variations in the following: (a) production of multiplemRNA species (4.5 kb, 5.3 kb, and 6 kb); (b) translation and/or stability of the AChE protein; (c) production of active and inactive AChE molecules; (d) production of amphiphilic and nonamphiphilic AChE forms; and (e) proportions of tetrameric G4, dimeric G2, and monomeric G1 forms. The large transcripts present distinct temporal patterns and disappear in the adult, which possesses only the 4.5-kb mRNA; these changes are unlikely to be related to those observed for the AChE protein, because all transcripts seem to encode the same catalytic subunit (type T). In addition, the levels of mRNA and AChE are not correlated in the three regions, especially at the adult stage. The proportion of inactive AChE was found to be markedly higher at the hatching period (E16) than at earlier stages (E10 and E13) or in the adult. The G4 form is pre-dominant already at E10, and in the adult its proportion reaches 80% of the activity in the cerebellum and optic lobes, and 65–70% in the neuroretina. This form is largely nonamhiphilic in embryonic tissues, but it becomes progressively more amphiphilic with development. Thus, the different processing and maturation steps appear to be regulated in an independent manner and potentially correspond to physiologically adaptative mechanisms.