AbstractThe nerve growth factor protein (NGF) has been identified by biological assay and rocket immunoelectrophoresis in media conditioned by monolayers of mouse S‐180 sarcoma cells, a transformed cell line of salivary gland origin. By utilization of a purification procedure designed to enrich for acid‐dissociable, high‐molecular‐weight complexes similar to the 7S‐NGF isolated from male mouse submaxillary gland, it has been determined that a significant portion of mouse sarcoma NGF is initially present as a complex at neutral pH with a molecualr weight indistinguishable from that of 7S‐NGF. At pH 4.0 the mouse sarcoma NGF complex dissociates, and the active subunit can be isolated as a species with a molecular weight of less than 40,000. The induced dissociation at pH 4.0 of the mouse sarcoma NGF high‐molecular‐weight complex, as well as the complex's behavior in isoelectric focusing and sucrose gradient sedimentation is consistent with the hypothesis that 7S‐NGF is packaged as a subunit containing protein intracellularly prior to secretion into the extracellular space. Moreover, the stability of the mouse sarcoma NGF complex at dilute concentrations is similar to that reported for the purifi