Although many kinds of nicotinic acetylcholine receptor (nAChR) subtypes have been reported in the neuronal tissues, subtype differences in the nAChR-mediated intracellular signaling remains obscure. Using nAChR agonists and antagonists, the involvement of nAChRs in extracellular signal-regulated protein kinase (ERK) phosphorylation in PC12h cells was investigated. Cytisine and nicotine induced the phosphorylation of ERKs in a dose-dependent manner, whereas RJR-2403 had no effect. Cytisine, but not RJR-2403, also induced phosphorylation of CREB. Mecamylamine, dextromethorphan and 18-methoxycoronaridine inhibited nicotine-induced ERK phosphorylation with much higher affinity than dihydro-beta-erythroidine and alpha-conotoxin MII. These results suggest the involvement of alpha3beta4 nAChRs in ERK phosphorylation in PC12h cells.