To investigate the mechanisms of areca quid (AQ)-induced carcinogenesis, expression of c-fos and c-jun protooncogenes was examined in human oral mucosal fibroblasts after exposure to areca nut extracts (ANE) or arecoline. We found that treatment of cells with 200 microg/ml ANE or 10 microg/ml arecoline for 1 h induced about three-fold increase in c-jun mRNA levels. This increase was transient and the level of c-jun mRNAs returned rapidly to control levels thereafter. However, ANE and arecoline did not induce c-fos mRNA expression at detectable levels. During AQ chewing, oral mucosal cells are continuously stimulated by ANE and arecoline. Persistent induction of the c-jun protooncogene by ANE and arecoline may be one of the mechanisms in the carcinogenesis of oral squamous cell carcinoma in Taiwan. Furthermore, we observed that pre-incubation of cells with either N-acetyl-cysteine [a glutathione (GSH) precursor] or L-buthionine-S,R-sulfoximine (a specific inhibitor of GSH biosynthesis) had a minimal effect on arecoline-induced c-jun expression. Therefore, arecoline-induced c-jun expression is independent of GSH depletion.