We recently demonstrated that insular cortex (IC) fetal implants supplemented by nerve growth factor (NGF) can accelerate the recovery of behavioral deficits induced by IC brain lesions. In the present report we describe results on in vivo assays of acetylcholine (ACh) turnover in the IC of rats subjected to the same brain lesion and implant treatments used in that research and for which detailed behavioral data are available. The neurochemical assays were carried out immediately after completion of the behavioral measurements. The assays showed that implants or NGF with heterotopic tissue continued to be associated with elevated levels of ACh and with deficits in learning and memory at a time postlesion when both behavior and ACh turnover in vivo, after treatment with homotopic implants and NGF combined, were at nonlesioned control levels. The results support the concept that, in vivo, the cholinergic neurotransmitter system is intimately involved in recovery from IC lesion-induced deficits in behavior and show that a combination of homotopic implant and NGF may be used as a means of manipulating that system to accelerate the repair of such deficits. Mechanisms by which this combination produces its effects are considered and the possibility is suggested that other neurotrophic factors (NTF) may also be useful when other types of brain lesions are involved.