Abstract: Specific peptides, and derived ionization characteristics of the peptides, from the Receptor Tyrosine-Protein Kinase erbB-4 Protein (HER4) protein are provided that are particularly advantageous for quantifying the HER4 protein directly in biological samples that have been fixed in formalin by the method of Selected Reaction Monitoring (SRM) mass spectrometry, or what can also be termed as Multiple Reaction Monitoring (MRM) mass spectrometry. Such biological samples are chemically preserved and fixed where the biological sample is selected from tissues and cells treated with formaldehyde containing agents/fixatives including formalin-fixed tissue/cells, formalin-fixed/paraffin embedded (FFPE) tissue/cells, FFPE tissue blocks and cells from those blocks, and tissue culture cells that have been formalin fixed and or paraffin embedded.