When a body has to adapt to changed conditions or recovers from a disease, proteins change in body fluids or organs. Therefore proteins could serve as biomarkers for the health of an individual. So called proteomics is an analytical method with high resolution, allowing investigation of these complex protein changes and detection of concentration changes of single proteins. This is outlined in the thesis and with a specific example (the effects of the flame retardant HBCD), it is illustrated what proteomics can contribute in the field of toxicological research. The research revealed that low doses of HBCD fed to rats for one week affected liver proteins only in female rats, not in males. Based on proteomics the mechanism behind this gender-specific effect could be understood. Results underline the importance of performing studies both in females and males, and show that the high sensitivity of proteomics allows finding gender-specific differences.