The overexpression of EGFR and/or HER-2 is associated with tumor cell resistance to chemotherapy, radiotherapy, disease progression and poor prognosis in patients with a variety of malignant tumors. Treatment combining the EGFR-targeting drug, gefitinib (ZD1839, Iressa) with the HER-2-targeting drug, trastuzumab (Herceptin) has been reported to improve therapeutic efficacy in patients with breast cancer. The purpose of this study was to examine the antitumor effect of this combination on head and neck squamous cell carcinoma (HNSCC) in vitro. Cell proliferation was inhibited significantly in two cell lines. Although IC50 of gefitinib alone against some cell lines was not reached, it was achieved after being combined with trastuzumab. Furthermore, IC50 was lower for the combination than for gefitinib alone in several cell lines. These results suggest that the combination may improve efficacy against HNSCC.