The detection of the character and quantity of specific sets of proteins in blood samples. Protein profiling has been used as a means of diagnosing specific illnesses, especially cancers or infectious diseases known to release unique protein patterns into serum. Protein profiling may be used as a means of screening for cancer recurrence in previously treated patients or in patients with multiple risk factors for an illness. It may also aid in the crafting of therapies, e.g., by demonstrating that a particular disease is susceptible to a specific drug therapy.