Irradiation tests of the transmutation of the fission products technetium and iodine are performed in the High Flux Reactor at Petten. Samples of technetium metal (99Tc) and of three different metal iodides (cerium triiodide, sodium iodide, and lead diiodide, containing the stable 127l isotope) are irradiated during eight reactor cycles (192.95 full-power days, corresponding to a neutron fluence of 2 × 1026 m-2). Postirradiation examination is performed to measure the transmutation rate and to investigate the material behavior during irradiation.