Dose-response curves of ibandronate (Iban from 10-6 to 10-3 M) in combination with increasing concentrations of 4-hydroxytamoxifen (TAM from 10-10 to 10-7 M) or ICI 182,780 (ICI from 10-10 to 10-7 M). MCF-7 cells were incubated for 72 hours. Cell proliferation was determined by crystal violet staining assay. Data are presented as percentages of control values (mean) and were used for combination index calculations (see Table 2). Experiments were performed three times in replicate.