The mean temperature of commercially pure aluminium slabs, upquenched in a heat treatment bath and (down) quenched in water, was determined theoretically and experimentally ; analysis and experiment were found to be in close agreement. The same theoretical approach was then used to estimate the relative times for different specimens to absorb the same amounts of heat energy. The assumption that geometrically different specimens of the same degree of cold work require the same amount of specific heat energy input to effect recrystallization was made. Thence, with the aid of experimentally determined times for complete recrystallization of specimens of any given thickness, each with different amounts of prior cold work, the theory was employed to predict recrystallization times for Eipecimens of different thicknesses but with the same amounts of cold work. In this way, the times for recrystallization of any specimen, for given material and upquench and quench bath conditions, with any amount of cold work, were determined (given experimentally determined times for recrystallization of specimens at the various amounts of cold work). Again analysis and experiment were found to agree closely.