Although reactions in substrate suspension are employed in industry for several bioconversion processes, there appears to be no quantitative model available in the literature to rationalize the optimization of these processes. We present a simple model that incorporates the kinetics of substrate dissolution and a simultaneous enzymatic reaction. The model was tested in the β£-chymotrypsin-catalyzed hydrolysis of an aqueous suspension of dimethyl benzylmethylmalonate to a homogeneous solution of enantiomerically pure monoester. This reaction occurs in the bulk phase, so catalysis by enzyme absorbed at the solid-liquid interface plays no role. The value of the parameters in the model (i.e., the mass transfer coefficient of substrate dissolution (k L ), the substrate solubility, and the rate constant for the enzymatic reaction) were determined in separate experiments. Using these parameter values, the model gave a good quantitative prediction of the rate of the overall dissolution-reaction process. When the particle size distribution is known, k L may also be calculated instead. The model seems to be applicable also for other poorly soluble substrates, other enzymes, and other solvents. Β©