Cisplatin, carboplatin, 5-fluorouracil and methotrexate concentrations in head and neck cancers are collected by in vivo microdialysis. The Pt concentration is subsequently analysed by means of HR-ICPMS. A speciation by online coupling of a chromatographical system to the HR-ICPMS is planned. Aims of the study: 1. To describe the time versus concentration profile in tumor tissue of the study drugs as a measure of tumor exposure. 2. To compare the tissue/plasma ratios as a measure of tumor penetration. 3. To describe the time versus concentration profile in the subcutaneous adipose tissue for the study drugs as a measure of drug exposure of normal tissue.