This study evaluated the effects of a combination of opioid growth factor (OGF) and paclitaxel on squamous cell carcinoma of the head and neck (SCCHN) using a tissue culture model of human SCCHN. The combination of OGF and paclitaxel was markedly inhibitory to SCCHN proliferation, reducing growth from control levels by 48 to 69% within 48 h. OGF in combination with carboplatin also depressed cell growth. The effect of a combination of OGF and paclitaxel or carboplatin on SCCHN growth was greater than either of the individual compounds. The efficacy of OGF, but not paclitaxel, was mediated by a naloxone-sensitive receptor and completely reversible. OGF, but no other endogenous or exogenous opioid, altered replication of SCCHN. OGF and paclitaxel depressed DNA synthesis, whereas only paclitaxel induced apoptosis. The combination of OGF and paclitaxel also had a supra-additive effect on the growth of another SCCHN, CAL-27, indicating the ubiquity of the combined drug activity. These data suggest that the combination of a biotherapy (OGF) and chemotherapy (paclitaxel and carboplatin) may provide an enhanced antitumor effect with respect to SCCHN.