Pharmaceutical development of peptide and protein drugs presents new problems in the area of stability assessment.Generally, these products require more anal. effort than more classic drugs; this may even dictate the speed of products require more anal. effort than more classic drugs; this may even dictate the speed of progress in certain development phases.As shown on the work on the hexapeptide Org 30035, a straight-forward strategy that has proven successful in this respect is discussed.Structures of all products present in relative quantities >0.5% were assigned.Hydrolysis was the main cause of degradationHowever, some unexpected oxidations also contributed significantly to the decomposition of the peptide.With regard to protein drugs, the initial phase of pharmaceutical development, the (pre) formulation studies, was studied..Although numerous covalent and non-covalent processes determine protein stability, it is proposed that in this phase only three protein characteristics need to be monitored, namely activity, size and charge.For the anal. of the latter two phys. parameters, simple and rapid electrophoretic techniques exist.By using these techniques together with activity-test sufficient information can be gathered in a rapid fashion which enables efficient evaluation and selection of test-formulations for further development.Examples are shown that were obtained during the development of a monoclonal antibody.