AbstractD–T operation of JET is currently programmed for mid-1991 onwards. An active gas handling plant to extract hydrogen isotopes from the torus exhausts and provide individual isotope feeds is being constructed. Although Torus Systems, additional heating systems and diagnostics have been designed for the tritium operation, their designs are presently subject to a detailed review. Some of the systems in direct contact with tritium will require modifications to improve their reliability and these modifications are being designed. Approval from safety and regulatory authorities is necessary to start operation with tritium, and to satisfy these requirements, analysis is being carried out of routine and accident conditions, waste arising and compatibility of systems with tritium operation. It is concluded that in parallel with the continuing successful experimental programme of JET in the D-D phase, the review of all aspects of the JET design and operation for the D-T phase is proceeding satisfactorily and no insurmountable problems are foreseen. The complete JET cycle will have a negligible environmental impact and the measures taken will ensure that radiation doses to workers are low.