The tritium balance based on pressure measurements has been performed on a shot by shot analysis during the plasma operations of the DTE1 campaign carried out at JET in 1997. This gives a complementary analysis to the integrated tritium inventory already reported for a full day of experiments. The particle balance shows that the T flux retention was of the order of about 1.26 1021 T s-1 during the plasma operations (~65% of the injected flux) . The outgasing between pulses reduces this T inventory to about 30% of the injection. This detailed gas balance shows also that the retention of hydrogen species depends on the plasma isotopic ratio. However, during the D clean up pulses, the amount of T removed by isotopic exchange is shown to be limited to about 2 1023 particles. Finally, the total particle balance (D+T) is shown to be independent the plasma isotopic ratio.