The movement of inclusions in casting has been studied using radioactive labelling of ceramic particles, a process known as positron emission particle tracking (PEPT). Alumina and silica particles of size about 355-710 mu m were made radioactive in a cyclotron, by the partial conversion of oxygen to F-18. This isotope has a half-life of 110 min, giving a window of time of around 3 h in which the particles could be detected by this technique. Individual radioactive particles were placed in ceramic moulds at known initial positions, which were then filled with low carbon steel, causing the particle to be entrained into the metal stream during the casting process. After the casting had solidified, the final position of the radioactive particle was determined using a gamma-ray positron camera. The initial and final co-ordinates of the deliberately entrained inclusions within the casting could then be obtained, with an accuracy of around 5 mm.