Increasingly, peptides are being used as therapeutic agents. Stabilization and recovery of a peptide drug from blood or plasma is critical to establishing a validated bioanalytical assay. As an example, we outline several processes that were evaluated to stabilize and recover a prototype peptide from plasma or blood. Stabilization entailed the rapid inhibition of proteolytic degradation of the peptide to allow for adequate sample collection and processing times from the biological fluid of interest. Once stabilized in these matrices, we were able to validate an HPLC/MS/MS method for the quantitative analysis of this peptide. The optimized stabilization and recovery method provided for a lower limit of quantitation that was <10 ng/mL. This method was shown to be accurate (107%) and precise (7%). To date, this HPLC/MS/MS assay has been used to analyze >1000 samples for the determination of the peptide levels in rat, dog, rabbit and human studies.