Rate equations for consecutive irreversible reactions such as are encountered in coupled enzyme assays are solved. For an assay containing one auxiliary enzyme, an expression is derived relating the time required to produce a linear reaction velocity and the amount of coupling enzyme added. The more complicated system in which two auxiliary enzymes are used required a graphical analysis. A nomogram is presented which shows the dependence of each coupling enzyme on the other in producing a linear reaction rate. Practical considerations for implementing these results are discussed with a view toward conserving auxiliary enzymes, saving the investigator's time, and increasing his confidence in results obtained from coupled assays. © 1969, American Chemical Society. All rights reserved.