In 2001 a multicenter randomized trial was initiated comparing accelerated radiotherapy with carbogen and nicotinamide as hypoxic modifiers against accelerated radiotherapy alone in patients with carcinoma of the larynx. This trial is approved and supported by the Dutch Cancer Society and currently 6 Dutch and 1 British center are participating. This trial provides a unique opportunity to prospectively test oxygenation and proliferation related marker profiles in a large homogeneous patient population and to assess the predictive capacity in a comparative setting with one group of patients receiving a hypoxia modifying treatment and the other group not.