PC12 cells, a widely used model neuronal cell line, are usually cultured in serum-supplemented medium. This report describes a serum-free medium for the culture of PC12 cells. PC12 cells grown in the two media types had similar growth rates and released dopamine in response to high potassium-induced calcium elevation. However, the levels of dopamine and of dopamine release in cells cultured in the serum-free medium were less than 10% of that in cells cultured in serum-supplemented medium. Dopamine levels recovered within 10 days if cells were returned to serum-supplemented medium, but dopamine release could not be recovered. Nerve growth factor (NGF) induced similar responses in PC12 cells cultured in both media, including phosphorylation of extracellular signal-regulated protein kinases and neurite extension. Transferrin was necessary for survival of neurite-bearing PC12 cells subcultured in serum-free medium and insulin promoted the cells proliferation. Ten days culture with NGF produced a similar increase in neurofilament expression and acetylcholinesterase activity in both media. These results suggest that PC12 in the hormonally defined serum-free media are qualitatively the same as those cultured in serum-supplemented media, and therefore this new culture protocol should enable more precise studies of PC12 cells culture in the absence of confounding unknown factors.