The cytotoxic effects of ethylcholine aziridinium ion (AF64A) were studied in primary cultures prepared from either whole brain, septum, or midbrain of fetal rats. AF64A, at concentrations up to 22.5 microM, significantly reduced the number of acetylcholinesterase-stained cells without affecting the number of dopaminergic neurons or their ability to take up and release [3H]dopamine. Many of the survived acetylcholinesterase-stained cells appeared with intact somata but damaged processes, indicating a retrograde degeneration starting at the nerve terminal. Higher concentrations of AF64A (greater than 22.5 microM), caused general toxicity which was expressed by degeneration of various neuronal and glial cells. Choline (500 microM), significantly protected the cells from AF64A induced cytotoxicity. The results are consistent with a previously described kinetic model, that predicted a dual action of AF64A: selective cholinotoxicity at low concentrations and non-selective cytotoxicity at higher concentrations.