Human serum contains thousands of proteolytically derived low-molecular-weight peptide fragments (serum peptidome). The concept of utilizing the serum peptidome for cancer diagnosis has been developed. A pathological serum peptidome appears when the homeostatic balance between proteases and protease inhibitors is disrupted. We hypothesize if analyses of the serum peptidome are of diagnostic value as information on which molecules are disrupted, and the pathological course it will take in unknown pathological conditions and disseminated intravascular coagulation (DIC). We analyzed the serum peptidome in 3 stages (early stage, pre-DIC and DIC stages) in one patient with POEMS (polyneuropathy, organomegaly, endocrinopathy, M protein and skin changes) syndrome, an intractable disease with unknown pathology, using a 1-dimensional gel electrophoresis/matrix-assisted laser desorption/ionization-mass spectrometry (1-DE/MS)-based rapid quantitative approach. A very large number of peptide fragments appeared in the DIC stage, compared to pre-DIC. In addition, we identified fragments of transthyretin (ALGISPFHEHAEVVFTANDSGPR, m/z 2451.18) and alpha1-antitrypsin (EDPQGDAAQKTDTSHHDQDHPTFN, m/z 2691.02) that significantly increased in the DIC stage, compared to those in the pre-DIC stage. Rapid analyses of the serum peptidome may lead to a diagnostic method that can predict on-going protease activated pathological conditions and help to decide on multilateral strategies including nutritional support and drug therapy.