A primary dissociated cell culture of Drosophila larval central nervous system is reported. Divisions of neuroblasts and vigorous outgrowth of neurites could be observed in culture. Within 24 hr cultured cells exhibited characteristic neuronal morphology and unimpaired ability to synthesize and accumulate acetylcholine. This cell culture system renders easy access to experimental analysis of normal neuronal properties and the altered mechanisms in neurological mutants. Single-channel currents induced by acetylcholine and regenerative action potentials were studied in the somata of the dissociated neurons. The appearance of Na channels in these cultured neurons was demonstrated by the cell lethality induced by veratridine and inhibition of the effect by tetrodotoxin. Dissociated neurons from a temperature-sensitive paralytic mutant napts, in which nerve conduction fails at high temperature, were studied in culture. Neuronal growth was not affected by this mutation, nor by tetrodotoxin. However, napts neurons showed greatly reduced sensitivity to veratridine even at 21 degrees C, a temperature at which napts individuals behave normally. This finding indicates expression of the napts phenotype at a level of isolated single cells and provides independent evidence that napts affects Na channel function.