A kinetic method, based upon measuring the transient time of coupled reactions, is proposed for the determination of the intermediate channel efficiency in a system of functionally interacting enzymes. The procedure rests upon a novel description in which the transient time is expressed as a function of channel efficiency and lifetime of the intermediate molecules. By this approach the reduction of transient time can be explained even if no changes in the kinetic parameters of the individual reactions occur. For determining channel efficiency, a linearized form has been evaluated and applied to the analysis of the kinetics of the aspartate aminotransferase-glutamate dehydrogenase coupled reaction, for which the data were taken from the literature [(1982) Eur. J. Biochem. 121, 511-517].