Rheumatoid arthritis (RA) is characterized by proliferation of synoviocytes that produce proinflammatory cytokines, which are implicated in the pathogenesis of RA. When human fibroblast-like synoviocytes line MH7A was treated with cigarette smoke condensate (CSC), either mainstream or sidestream, expression levels of interleukin (IL)-1alpha, IL-1beta, IL-6, IL-8, and CYP1A1 mRNA were upregulated in both time- and dose-dependent manners. The upregulatory effects of CSC on these cytokines were not significantly inhibited by alpha-naphthoflavone, an aryl hydrocarbon receptor (AhR) antagonist, suggesting that the effects of CSC were independent of AhR. Cycloheximide treatment indicated that the augmenting effect of CSC on IL-1alpha, IL-1beta and IL-8, but not IL-6 and CYP1A1, mRNA expression requires de novo protein synthesis. CSC also induced cytokines at protein levels and further augmented the effects of tumor necrosis factor alpha on induction of these cytokines at both mRNA and protein levels. These results support the epidemiological studies indicating a strong association between heavy cigarette smoking and pathogenesis of RA.