The design of treatment for patients with squamous cell carcinoma of the head and neck (SCCHN) is based on prognostic factors, today essentially performance status and TNM status. It becomes increasingly important to optimise treatment and find the appropriate level of treatment and resource consumption for each patient. This can be achieved by means of complementary "biological staging' using predictive factors. A predictive factor contains prognostic information but can also be used to choose between alternative treatments. Candidate variables for prediction of the outcome of chemotherapy are tumour ploidy status, the level of circulating C1q-complexes, the level of p53 expression, and resistance/sensitivity measured by in vitro assays. Several variables and assays capable of predicting response to radiotherapy have been proposed, e.g. the surviving fraction 2 Gy (SF2), potential tumour doubling time (Tpot), and the micronucleus assay. As none of these have yet proved to be of clinical value in a prospective randomised trial, continued studies are well worthwhile.