The project’s aim was to develop and test the applicability of a method to determine the presence of serum immunoglobulins against specific autoantibodies. The method combined immunoglobulin G enrichment (using Melon Gel), molecular weight filtration, and targeted mass spectrometry and the feasibility was successfully tested in an experiment using a peptide library (tryptic digest) of dinitrophenyl labelled peptides and anti-DNP. In a second step, a phospho-peptide library, derived from glioblastoma multiform tissue, was tested against plasma samples from glioma patients and healthy donors, to determine the presence of complexes of IgG with immunoaffinity to EGFR or GFAP phospho-peptides. As a result, we found immunoaffinity to EGFR phospho-peptide GSHQIS[+80]LDNPDYQQDFFPK (covering the phospho-site S1166) in plasma of glioma patients.