The aim of the present study was to develop suitable and reliable method for quantification three of the most worldwide used therapeutic monoclonal antibodies (mAbs) -bevazizumab (BVZ), infliximab (INF) and trastuzumab (TTZ)- to be used in long-term stability studies. Reverse phase (RP) was selected by its greater sensibility and reproducibility comparing with other chromatographic modes. Then a high performance liquid chromatography with diode array detection (RP)HPLC/DAD method was checked. Since the three mAbs represent the active ingredient in the medicines in which they are formulated, the selected method was validated for each one in accordance with the International Conference on Harmonization (ICH) guidelines for pharmaceuticals for human use. Then method was validated in terms of linearity, accuracy, precision, (repeatability, intermediate precision) specificity (by forced degradation studies), robustness and system suitability. Spectral peak purity analysis strategy was used to test mAb degradations. Comparative study of the results indicated similar behavior for the three mAbs. Forced degradation studies also provided deep knowledge of these important bio-macromolecules. At last the method was successfully used to quantify BVZ, INF and TTZ in long-term stability studies performed under hospital conditions of use and they showed great stability regarding quantification during the time of the study.