We have previously shown that treatment of cultured dorsal root ganglion neurons (DRGN) with a highly specific, reversible acetylcholinesterase (AChE) inhibitor, BW284c51, retards neuritic outgrowth in a dose dependent manner and is accompanied by the presence of abnormal, perikaryal neurofilament (NF) inclusions in approximately 40% of the cells. Since subpopulations of DRGN have been classified according to their levels of AChE activity, we have combined immunocytochemical and enzyme histochemical techniques to investigate a possible correlation between AChE activity and the presence of NF inclusion formation. Our results show that after inhibitor treatment, cells with low levels of AChE activity have a greater percentage of inclusions, with nearly 75% of cells with undetectable levels of AChE activity containing inclusions. In contrast, inclusions were present in only 3.2% of cells with high levels of AChE activity. This inverse relationship between AChE activity and the presence of NF inclusions supports our previous observations that this enzyme may have extra-synaptic functions which could affect neuronal development and regeneration.