A daunorubicin (DNR)-resistant variant (AH66DR) of alpha-fetoprotein (AFP)-producing rat ascites hepatoma AH66 was established. AH66DR was 169 times more resistant to DNR than AH66. A growth-inhibitory effect due to the decrease in sugar uptake following treatment of the cell lines with specific antibody against highly purified rat AFP was also observed. Pre-incubation of both lines with antibody prior to the measurement of 2-deoxy-D-glucose (2dG) uptake resulted in a 45-55% decrease in 2dG uptake compared to control cells with a 2-fold reduction of Vmax value while the Km remained unchanged. Upon pre-incubating AH66DR with antibody, an increased intracellular level of DNR concentration with reduction of efflux rate was observed. A significantly superior cytotoxic effect against AH66DR, which reached almost the same level as the cytotoxic effect of DNR against AH66, was found, as compared to various other controls when tumor cells were cultured with a mixture of antibody and DNR. Our in vitro results suggest that the DNR-resistance of the AFP-producing tumor cells may be overcome if the cells are treated with specific antibody.