AbstractAlthough chemotherapeutic drugs are frequently administered to patient with osteosarcoma, there has been little research into the effect of cytotoxic drugs on osteosarcoma cell biology. The effect of two drugs (Adriamycin and bleomycin) on cell cycle kinetics was investigated in vitro in an established line of human osteosarcoma cells and in vivo using the Dunn osteosarcoma model. The cell cycle changes were consistent with G2arrest for both drugs in vivo and in vitro. The alteration in cell cycle distribution was correlated with inhibition of3H‐thymidine incorporation in vitro. In vivo, the greater change in cell cycle distribution caused by Adriamycin was reflected in the increased inhibition of tumor growth found with this dru