The release kinetics of beta-galactosidase protein have been determined during small-scale ultrasonication of E. coli cells. Among several studied parameters, ionic strength and cell concentration have the least influence on the rate of protein recovery, whereas sample volume and acoustic power dramatically affect the final yield of soluble protein in the cell-free fraction. The analysis of these critical parameters has prompted us to propose a simple model for E. coli disintegration that only involves acoustic power and sample volume, and which allows prediction of optimal sonication times to recover significant amounts of both natural and recombinant proteins in a given set of relevant conditions.