Because of the high interannual and seasonal variability, transports from the various methods used to estimate the Indonesian throughflow encompass a large range of values. Here, we estimate a temporally integrated transport for the throughflow from comparison of the tritium water column inventory on both sides of the throughflow. Our approach is based on the simple idea that tritium, with a radioactive decay half-life of 12.32 yr, is well suited to infer the transit time (and consequently the mass flow) of the waters through the Indonesian archipelago. We show that the tritium budget implies a flow of 8.6 ¿ 4 Sv, corresponding to a transit time of 10.5 yr. This result, which represents an average over seasons and several ENSO and non-ENSO periods, shows that repeated tritium measurements on both sides of the Indonesian Seas could provide a useful method for monitoring the long-term evolution of the throughflow.