The invention relates to a microfluidic system for controlling a concentration profile of molecules capable of stimulating a target, for example formed by an assembly of living cells, this system comprising: —a microfluidic device (1) comprising at least one microfluidic channel (4) equipped with at least one inlet orifice (21) and with at least one outlet orifice (22) for at least one fluid; —at least one means for supplying the microfluidic channel (4) with at least one fluid comprising molecules capable of stimulating the target; —at least one chamber (8) or another microfluidic channel comprising a base (6) intended to receive the target; and —at least one microporous membrane (5) separating the chamber (8) or the other microfluidic channel from the microfluidic channel (4), said microporous membrane (5) being positioned away from the base (6) so that when the supply means provides the microfludic channel (4) with said at least one fluid flowing in laminar flow in contact with the microporous membrane (5), the molecules capable of stimulating the target then diffuse, after having passed through the microporous membrane (5) through the chamber (8) or said other microfluidic channel in order to finally form a stable concentration profile in this chamber (8) or this other microfluidic channel.