The performance of an adiabatic tubular reactor under permanent transient conditions forced through the reversal flow of the reaction mixture (switch flow) in reference to the steady state operation has been analysed. Two cases when both a parallel, first-order, reaction system of the A -> B, A -> C type and a consecutive first-order reaction system of the A -> B, B -> C type occur have been considered. A simplified numerical method has been used for solving the balance equations of the reactor.