A human hybrid neuronal cell line A1 has been generated by somatic fusion between a human fetal cerebral neuron and a human neuroblastoma cell, and RT-PCR, immunochemical, and electrophysiological studies of the hybrid cells indicated that the cells express faithfully of morphological, immunochemical, physiological, and genetic features of human cerebral neurons. A1 hybrid neurons express neuron-specific markers such as neurofilament-L (NF-L), NF-M, NF-H, MAP-2, and beta tubulin III. A1 human hybrid neurons express messages for various cytokines and cytokine receptors which are similar to parental human CNS neurons and different from the other parental cell line, SK-SH-SY5Y neuroblastoma. A1 hybrid neurons also express messages for choline acetyltransferase (ChAT), tyrosine hydroxylase (TH), and glutamic acid decarboxylase (GAD), indicating that they could differentiate into various subsets of neuronal types. Whole-cell patch clamp experiments showed that A1 hybrid neurons expressed Na+ currents, which were completely blocked by tetrodotoxin. In addition, depolarizing and hyperpolarizing voltage clamp steps evoked respective outward and inward K+ currents in these cells. When A1 hybrid neurons were exposed to beta amyloid for 72 hr, there was three-fold increase in TUNEL positive cells over controls, indicating that beta amyloid is neurotoxic to A1 hybrid neurons. The present study indicates that the A1 human hybrid neuronal cell line should serve as a valuable in vitro model for studies of biology, physiology, and pathology of human neurons in health and disease.