In this study the dose-response curves for doxorubicin, pirarubicin, 5-fluoro-uracil, 4-hydroperoxy-cyclophosphamide and taxol were obtained in three breast cancer cell lines (MCF-7, T47D and BT-20). The ATP cell viability assay was chosen to evaluate the chemosensitivity profiles and was a reproducible, practicable method to assess drug response in breast cancer cell lines. The IC50 values were calculated on the median effect principle and indicated that taxol was the most active drug tested in this study with a mean IC50 value of 0.02 μM. This in vitro effect correlated well with clinical observations in metastatic breast cancer where taxol proved to be a very active drug. Pirarubicin was the second most active drug tested with an IC50 value 10 times less compared to that of doxorubicin. The results obtained with the ATP cell viability assay are promising, therefore further testing with drug combination chemotherapy and fresh human breast cancer tumor testing are warranted and ongoing