Mutations in Cu/Zn-superoxide dismutase (SOD1) gene have been identified in familial amyotrophic lateral sclerosis. Motor neuron degeneration subsequently spreads to contiguous neurons of the motor systems. We developed an in vitro disease model with motor neuron-neuroblastoma hybrid cells (VSC4.1) constitutively expressing a mutant (G93A) SOD1. The extracellular effect upon adjacent motor neurons was determined using the substratum culture insert. The viability of VSC 4.1 was lowered by 26% in a co-culture of VSC 4.1 and G93A, which was reversed by Trolox, an antioxidant. This in vitro disease model confirmed the extracellular toxicity of the mutant SOD1 cells on the adjacent neurons by generating oxidative stress.