The biological activities of recombinant human nerve growth factor (rhNGF) produced by Chinese hamster ovary (CHO) cells that were transfected with human NGF gene were investigated in vitro and in vivo. rhNGF showed the same immunoreactivity as mouse NGF (mNGF) in a highly sensitive two-site enzyme immunoassay system employing mouse monoclonal antibody against mouse beta-NGF (MAb 27/21) for both the primary and the secondary antibodies. In PC12 cells, rhNGF promoted neurite extension and induced acetylcholinesterase (AChE) with the same potency as mNGF, showing an ED50 of 10-20 ng/mL. In fetal rat septal neurons cultured on a feeder layer of astroglial cells, rhNGF promoted survival and neurite extension as well as an increase in choline acetyltransferase (ChAT) activity and acetylcholine (ACh) content. At a maximal effective concentration of 30 ng/mL, rhNGF promoted a 1.4-, 2.8-, and 4-fold increase in surviving cell number, ACh content, and ChAT activity, respectively. rhNGF was five times more potent than mNGF for the increase in ChAT activity and ACh content showing an ED50 of 0.5 ng/mL, although the maximal response was the same for the two NGFs. Transection of the fimbria-fornix resulted in a loss of AChE-positive cells in the medial septum (MS) and vertical limb of the diagonal band of Broca (VDB). The administration of rhNGF or mNGF (3 or 30 micrograms in gel form) attenuated the loss of AChE-positive cells; rhNGF was as potent as or even more potent than mNGF. Radio frequency lesion of the basal forebrain (BF) including the nucleus basalis magnocellularis (NBM) resulted in severe impairment of memory and/or learning in passive avoidance and Morris' water maze tasks. Repeated injection of rhNGF (5 micrograms x 5 over 2 wk) into the lateral ventricle ameliorated the behavioral impairment in the water maze task but not in passive avoidance. rhNGF treatment increased ChAT activity in the frontal cortex and even in other subregions of the cerebral cortex where ChAT activity was not decreased by BF lesion. These results indicate that human NGF can be measured in an enzyme immunoassay system using monoclonal antibody against mNGF (MAb 27/21) and that rhNGF has potent biological activity, comparable to or greater than mNGF, both in vitro and in vivo.