Molecularly Imprinted Polymers (MIPs) are tailor-made polymers with high affinity for a specific target. They can be used for selective sample preparation prior to liquid chromatography mass spectrometry determination of target analytes. In this master thesis the reusability of magnetic MIPs (mMIPs) targeting the signature peptide NLLGLIEAK of the small cell lung cancer biomarker progastrin releasing peptide was evaluated. Reuse of mMIPs could save time and money used for production of new mMIPs. Previously used mMIPs were washed overnight. Two wash solutions, MeOH:0.1M HCl and 100 % MeOH and a couple of different conditioning procedures were evaluated with the goal to get efficiently washed mMIPs that performed with high reproducibility. Reusability of washed mMIPs was evaluated according to the following parameters: remaining peptide after wash, binding efficiency and elution recovery. Remaining peptide was determined by performing blank extractions using mMIPs washed by both washing procedures. No signal was seen using any of the wash solutions suggesting that both wash solutions efficiently removed non-eluted peptide. The binding efficiency was determined to more than 99 % and considered satisfactory for reuse of the MIPs. Finally, elution recoveries were determined. These were seen to be lower and more variable compared to when using new mMIPs. There were no significant difference in results gained from washed mMIPs with different solutions and under different conditions. In addition, in a final experiment the washed mMIPs were evaluated for use in extraction of the target peptide from protein precipitated serum. The washed mMIPs were able to extract from complex biological matrices but the elution recoveries (5.8 ± 0.6%) were lower and repeatability was poorer than seen for new mMIPs (17.1 ± 8.6%).