The growth of tumor cells can be regulated by a variety of cytokines. To investigate the pathogenesis of head and neck cancer and explore a new therapeutic approach for the carcinoma, the role of interleukin-6 (IL-6) in the growth of a human head and neck squamous cell carcinoma (HNSCC) cell line was examined. Whether or not IL-6 is increased in HNSCC and whether or not IL-6 antisense oligonucleotide treatment could decrease proliferation and angiogenic activity of HNSCC cell lines, was determined. Established human HNSCC cell lines were screened for IL-6 expression at both mRNA and protein levels. By using a 15-mer antisense phosphorothioate oligonucleotide targeting a sequence in the second exon of the IL-6 gene, modulation of IL-6 and vascular endothelial growth factor (VEGF) expression was examined in UMSCC IIA in cell supernatants by capture enzyme-linked immunosorbent assay (ELISA), and in cell lysates by reverse transcriptase-polymerase chain reaction (RT-PCR). In addition, cell growth was determined by cell count. Endothelial cell migration was measured using a modified Boyden chamber. IL-6 was identified in the supernatant of the cell culture medium, indicating that these cells secreted IL-6, and the mRNAs of IL-6 were shown to be present in the cell lysates. IL-6 antisense oligonucleotide treatment resulted in a significant reduction of IL-6 protein expression compared to the sense control. The antisense oligonucleotides targeting IL-6 mRNA, also, inhibited cell growth and IL-6 production as well as VEGF expression. The addition of conditioned medium from IL-6 antisense-treated tumor cells resulted in decreased endothelial cell migration and tubule formation. Taken together, these findings indicate that endogenous IL-6 plays an important role in the growth of HNSCC and exerts its action by an autocrine growth mechanism, and that therapeutic trials with antisense oligonucleotides targeted to IL-6 mRNA may have some value for the treatment of HNSCC due to a decrease of neovascularization.