Small,quantities of high-Z impurities have been injected into JET plasmas and their progression was followed with good spatial and temporal resolution using two soft X-ray cameras. The results show that the transport of impurities is much slower in the central region of the plasma than in the outside and that it is greatly enhanced during sawtooth crashes. Simulation of the evolution of the emissivity profiles using an impurity transport code yielded values for the radially dependent transport coefficients and in particular these values have been compared in the cases of ohmically heated and RF heated plasmas.