We present a simple and general reduction algorithm for stiff monomolecular kinetic systems. The reduction is based on algebraic techniques and consists in eliminating the fastest dynamics in the initial system without any change of basis. This process is systematic and is not based on chemical conventional assumptions or on singular perturbation techniques. Systems can be reduced even if they are not in the Tikhonov form. This reduction process is applied to kinetic systems with kinetic constants belonging to different scales. Error estimates for all species are given. Numerical tests are performed.§Part of this work was carried out during the 1997-1998 year at the Department of Mathematics at MIT, USA.