The aim of this study was to determine whether the ultrasound, with a dosage that did not lead to acute and delayed inhibition, could potentiate the cytotoxicity of adriamycin to human ovarian carcinoma cell line 3AO in vitro. Drug sensitivity was analyzed by clonogenic assay, cells were treated by adriamycin singly in group ADM (control), adriamycin prior to ultrasound exposure in group ADM US, and ultrasound irradiation prior to adriamycin administration in group US ADM. The intracellular drug accumulation in each group was determined by ¯uorometry. The results were: (1) the values of IC 50 were 0.0083, <0.001 and 0.0065 lg/ ml in group ADM, ADM US and US ADM respectively; the clone surviving rate in group ADM US and in group US ADM were decreased P < 0:001; P < 0:01, compared with control; the surviving rate in group ADM US was lower than that in group US ADM P < 0:01. (2) The intracellular drug accumulations in group ADM US were promoted P < 0:01 and not increased signi®cantly in group US ADM P > 0:05. These suggested that the low-level ultrasound could enhance the cytotoxicity of adriamycin to human ovarian carcinoma cells and promoted intracellular drug contents played the leading role.