Whole body hyperthermia is one of the methods available for the treatment of malignant turrours with heat. At the Rotterdam Radio-Therapeutic Institute this method was investigated in 27 patients in a period of 3 1/2 years. This thesis describes the results of this investigation. The final conclusions from this study are: the technique used for induction of WBHT is clinically useful and its efficiency is comparable to the efficiencies mentioned by other authors Who use a technique of transcutaneous energy input; - WBHT at 41.8°C for 2 hours is effective, but has to be canbined with either radiotherapy or cherrotherapy to obtain a valuable effect for the patient; In sane cases the treatment may unexpectedly induce severe toxicity. Therefore research should continue with regard to better alternatives such as local hyperthennia and/or a safer method of WBHI'-induction.