The effects on the performance of an air-detritiation dryer (ADD) of inlet-gas humidity and residual tritiated water (HTO) left on the desiccant following regeneration were demonstrated. Residual HTO significantly reduced the detritiation factor (DFSP) of an ADD from clean-bed values. In addition, HTO/H2O separation occurred in the ADD, with H2O leading HTO. HTO roll-up may also have occurred. Finally, an increase in the inlet-gas humidity at constant inlet HTO concentration decreased the DFSP while increasing the humidity-reduction factor (HRFSP).