We have studied the changes in acetylcholinesterase (AChE) molecular forms during cross-innervation of the inferior smooth muscle of the cat nictitating membrane by the hypoglossal nerve. One month after functional cross-innervation AChE activity increases by two-fold above control values, and a new high molecular weight AChE form (A12) is detected, BW284c51, an anti-AChE, potentiates the contraction of the cross-innervated smooth muscle. Three months later, AChE activity has raised six-fold above normal values. At this time, half of the activity sediments to the bottom of the sucrose gradient and a time-dependent dissociation occurs in lighter AchE forms, reminiscent of AChE aggregates observed in the electric eel. We discuss the possibility that the multimolecular aggregates are involved in the immobilizatin of AChE at the neuromuscular junction of a motor nerve and a smooth muscle.