Abstract Ammonia and ammonium ion uptake by layered inorganic ion exchangers is of interest for potential use in the removal of ammonia and ammonium ions from human blood (renal dialysis machines) or from waste solutions. Data reported in the literature on the titration of Zr(HPO 4) 2·H 2O with (NH 4Cl + NH 3·H 2O) solutions seem indicate that H + NH 4 + exchange is possible and that contrary to the behaviour toward alkali metal ions, both the protons of the exchanger are exhibiting the same pK value toward ammonium ion. A detailed investigation on the mechanism of the formation of Zr(NH 4PO 4) 2·H 2O in the titration of Zr(HPO 4) 2·H 2O showed that this formation is not due to a direct H + NH 4 + exchange but to an addition of ammonia to the protons of the exchanger. The lack of direct H + NH 4 + exchange on Zr(HPO 4) 2·H 2O was ascribed to steric impediments since this exchange can be acheived on polyhydrated dihydrogen forms of crystalline zirconium phosphate where the steric impediments are overcome owing to their large interlayer distance. The Na + NH 4 + ion exchange isotherm on Zr(NaPO 4)(HPO 4)·5H 2O and the K + NH 4 + isotherm on Zr(KPO 4) 2·3H 2O also have been investigated and discussed. Polyhydrated dihydrogen forms of zirconium phosphate seem to be good materials for removal of both ammonia and ammonium ions.