In a study involving 212 samples of surface and sub‐surface soils derived from basaltic, granitic, and metamorphic parent materials in the high rainfall region of north Queensland, Australia, the Al extracted with 1 M KC1 has been compared with ‘exchangeable aluminium’, defined as the difference between CEC and sum of basic exchangeable cations. It was concluded that for these highly weathered soils KCl‐extractable Al is exchangeable, and therefore that the sum of basic and acidic cations (ECEC) is a reliable measure of CEC at field conditions.