The processes involved in the release of silicon (Si) and aluminium (Al) from soils during extraction with 0.01M calcium chloride (CaCl2) were investigated. A considerable amount of Si was released from most soil samples studied during the first hour of extraction which continued steadily until the end of the experiment (144 hrs). Most Si was released from fine grained soils, least from sand. Uncomplexed and complexed Al was initially released rapidly, but after 1 hr net resorption of uncomplexed Al to the soil occurred. Aluminium concentrations appeared to reflect surface characteristics of the soil rather than control by a particular solid phase.