Attempts to control the raceway depth have been made with many different technologies however none of them have had the capability to measure during operation. By using microwave technology the problem with interfering obstacles such as the coal injection can be avoided since the technology is not susceptible to this kind of interference. In this paper a novel approach using microwave technology to measure the raceway variations during operation will be described. MEFOS, The Metallurgical Research Institute AB, Lulea, Sweden, has tested an especially developed microwave unit to continuously measure the variations of the raceway during operation in the Blast Furnace. The trials were performed as a single tuyère trial on Blast Furnace 3 at SSAB Tunnplat AB, Lulea, Sweden with excellent results.