Method for carrying out in continuous, under so-called pseudo-isothermal conditions and in a predetermined reaction environment, such as a catalytic bed, a selected chemical reaction, comprising the steps of providing in the reaction environment at least one tubular heat exchanger fed with a first flow of a heat exchange operating fluid at a respective predetermined inlet temperature, the fluid passing through the at least one tubular heat exchanger according to a respective inlet/outlet path, which method also provides the step of feeding into the at least one tubular heat exchanger and at one or more intermediate positions of said path, a second flow of operating fluid having a respective predetermined inlet temperature.