We have developed an original setup using microfluidic tools allowing one to produce continuously monodisperse microreactors (approximate to 100 nL), and to control their temperatures as they flow in the microdevice. With a specific microchannels geometry, we are able to apply large temperature quenches to droplets containing a KNO3 solution (up to 50 degrees C in 10 s), and then to follow nucleation kinetics at high supersaturations. By measuring the probability of crystal presence in the droplets as a function of time, we estimate the nucleation rate for different supersaturations, and confront our results to the classical nucleation theory. (C) 2007 Elsevier B.V. All rights reserved.