On the basis of the experimental works of Krummradt et al. (1999), this paper shows how it is possible, for certain systems of reactions. to reduce considerably the operations times from a semi-batch stirred tanks to a continuous microreactor, in which mixing and heat transfer are intensified. In the case of the Grignard reaction. we demonstrate that it is so possible to reduce the operation time from 5 h to less than 10 s. However, to reach the productivity of the industrial 6 in 3 stirred tank. it is necessary to use five minireactors in parallel. For such exothermic reactional systems, the field of interest for an intensified reactor use as an industrial production tool is specified.