Summary form only given, as follows. In the course of the preliminary tritium experiment (PTE) in JET, where combined D and T neutral beam injection generated a DT fusion power of 1.7 MW, ion cyclotron emission (ICE) in the frequency range up to 180 MHz was measured using an ICRF heating antenna as probe. The ICE spectrum showed a number of superthermal narrow, equally spaced emission lines which correspond to deuteron or alpha -particle ion cyclotron harmonics at the outer mid-plane edge (major radius R approximately 4 m). DD and DT power spectra are similar in form, and show split lines which, above approximately 100 MHz, merge into a continuum. With tritium injection, the ICE power increased by a factor comparable to the increase of neutron flux, indicating that 3.5 MeV fusion alpha -particles provide the free energy for generating ICE. The ICE power increases almost linearly with neutron flux over a range of six decades. The evolution of the ICE follows the rise of the neutron flux, but is delayed by a time comparable with the slowing-down time of the alpha -particles. The ICE intensity is anti-correlated with large amplitude edge-localized modes.