The transient state analysis of the consecutive sequence of reactions S → P1 → P2 taking place inside a porous spherical coimmobilized biocatalyst is discussed for the case in which each step follows Michaelis Menten type kinetics. The theoretical analysis includes intraparticle diffusional limitations. The model equations are solved by the explicit finite difference method. The effect of various parameters of importance on the batch reactor performance is discussed. Comparison of the model with experimental results has been shown. © 1994 Springer-Verlag.