Acetylcholine receptor ligands were studied for cytotoxicity in K562 human erythroid leukemia tumor cells. Cytotoxicity of carbachol, an agonist of acetylcholine receptors, atropine, an antagonist of muscarinic acetylcholine receptor, neurotoxin II (NT II) from Naja naja oxiana cobra venom and tubocurarine, antagonists of acetylcholine receptor of nicotinic type was exhibited in the 10-7-10-15 M concentration range. Several cytolytic processes, two for carbachol and three for other ligands, corresponding to different concentrations of each ligand were detected. All acetylcholine receptor ligands induced internucleosomal DNA fragmentation.