Four molecular forms of acetylcholinesterase (AChE) have been observed in extracts from ciliary ganglion and iris by gel electrophoresis followed by Koelle's reaction and densitometry on gels. Forms I, II, and III (order of anodic migration) are present in the 'soluble fraction' (SF) while forms II, III, and IV appear in the 'membranous fraction' (MF). 10 days after postganglionic axotomy in young chickens, the relative proportions of the membranous forms were changed in both the ciliary ganglion and iris, with a marked reduction of form IV occurring. A characteristic evolution of both the soluble and membranous forms of AChE was evident through different developmental stages (10th day of incubation; 2nd, 11th and 56th day posthatching). In the ciliary ganglion the faster components were reduced in favor of form IV. Conversely, the relative proportion of the faster components was increased in the iris. The observed changes in the AChE forms are compared with changes in the structure and function of these organs known to occur in the conditions under study. Evidence is presented which suggests a junctional localization for the form IV in both the ciliary ganglion and iris.