Abstract The JET Active Gas Handling System (AGHS) was designed, built and commissioned to handle radioactive tritium gas mixtures safely, to supply tritium (T2) and deuterium (D2) to the JET torus, to process the exhaust gases with the main purpose to enrich and re-use T2 and D2, to detritiate tritiated impurities and to keep discharges below the approved daily release limits. In addition, the AGHS had to supply the necessary ventilation air streams during maintenance or repair inside or outside of the AGHS building. During the first Deuterium–Tritium Experiment (DTE1) at JET in 1997 the AGHS fulfilled all these tasks in an excellent manner. No unauthorised or unplanned tritium releases occurred and no operational delays were caused by the AGHS. In fact, this was the first true demonstration that quantities of tritium in the tens of grams range can be recycled safely and efficiently in a large fusion device. At the start of DTE1 20 g of tritium were available on the JET site. About 100 g of tritium were supplied from the AGHS to the users which necessitated the recycling of tritium at least five times. Approximately 220 tritium plasma shots were performed during DTE1. Large amounts of tritium were temporarily trapped in the torus. This overview presents the performance of the whole AGHS during DTE1 as well as general aspects such as the preparation for DTE1; the quantities of gases supplied from the AGHS to the users and pumped back to the AGHS; tritium accountancy; interlock systems; failure of equipment; and gives detailed information of the gas processing in each subsystem of the AGHS. As a result of the performance of the AGHS during DTE1 we can state confidently that the AGHS is ready for further Deuterium–Tritium Experiments.