Although diagnostic systems for the tokamak fusion test reactor (TFTR) must be compatible with high‐power experiments in deuterium–tritium (D–T) plasmas, it has been neither possible nor desirable to implement all the required features during the early phases of the facility. The research plan, the physical plant, instrumentation, and diagnostic techniques have all evolved during the past decade, and some of the original plans are no longer suitable. Preparations are now underway for D–T operation in TFTR in 1990. Among the activities necessary in support of the research plan are completion of the installation of the D–T diagnostic set, modification of diagnostic hardware to accommodate the ‘‘igloo’’ radiation shield of the torus, installation of auxiliary shielding for detectors and electronics, and enhancement of the reliability of specific components. These preparations and the final D–T diagnostic set for TFTR will be described.