BOTH deprenyl and rasagiline (R(+)-N-propargyl-1–aminoindane mesylate), at a concentration of 1–1 μM, increased survival in vitro of rat E14 mesencephalic dopaminergic neurons that had been primed with 10% serum for 1 2 h (p < 0.05). Rasagiline, but not deprenyl, also increased total neuronal (MAP2–positive) survival (p < 0.05) Under serum-free conditions, rasagiline, but not deprenyl, retained its neuroprotective action on dopaminergic neurones. GABAergic neurons were not affected by either deprenyl or rasagiline. Clorgyline, an MAO-A inhibitor, did not exert any of these effects. The protective action of rasagiline on dopaminergic neurons, even under stringent serum-free conditions, is striking, and warrants further investigation for a role in the treatment of Parkinson's disease.