A regimen-dependent synergistic combination effect of both drugs was found in vitro. In animals, hepatic artery chemoembolization with GEM was superior to systemic intravenous bolus treatment. Portal vein chemoembolization with MTA was ineffective. The optimal in vitro regimen of MTA (intravenous or PVCE) preceding GEM (HACE) resulted in a maximally additive tumor growth inhibition. The results indicate that MTA and GEM can successfully be combined and favor further evaluation in patients.