A comparative study of the exchange behaviour of pyridinium, picolinium, lutidinium and collidinium salts of tungstophosphoric as well as of molybdophosphoric acid has been made. The exchange isotherms of both tungstophosphates and molybdophosphates against NH4+, K+, Na+, and Li+ clearly indicate that the exchangeability decreases with the increase in the size of the exchangeable ion in the heteropoly salts. Tungstosilicates having the same organic cations as mentioned above have also been studied. Out of the four salts of tungstosilicic acid, the solubility of only collidinium tungstosilicate is low enough to be studied as an ion exchanger. The collidinium ion in this salt can be exchanged by large cations viz., (CH3)4N+, (CH3)3NH+ and (CH3)2NH2+.