Tunicamycin (TM) is known to cause severe neurological diseases in the central nervous system of animals. Cultured cerebellar granule cells were used to investigate the direct cytotoxicity of this agent on cerebellar neurons. Results indicate that TM is a potent inhibitor of glycosylation and protein synthesis. This agent killed granule cells in a dose- and time-dependent manner. TM treatment of these neurons lead to atrophic cell bodies and condensed nuclei. This TM-induced cell death could be prevented by cycloheximide and aurintricarboxylic acid. In contrast, TM had no apparent toxicity toward nerve growth factor-differentiated PC12 cells under similar conditions. These results suggest that TM kills cerebellar granule cells in a manner similar to programmed cell death.