Abstract: The present invention pertains to a fluid microdiode for directionally incorporating a dosed fluid into another stationary or flowing target fluid contained in a closed system, especially in the submicroliter range. It is characterized by a planar arrangement of a microcapillary open on both sides or a system of closely juxtaposed microcapillaries open on both sides being in direct contact with the target fluid on the outlet side thereof and being separated from the discontinuously supplied dosed fluid on their inlet side by an air or gas cushion, forming a meniscus (6) which is curved according to the surface tension. As a device (1), said fluid microdiode consists of a stacked arrangement of a flow channel (9), the actual diode in the form of a grid structure formed by capillaries, and a spacer chip (2), securing the gaseous medium in the region of the coupling surface.