Pressure-operable microfluidic structure for the bubble-free combining of two liquid volumes with a fluid chamber that has a feed opening, as well as an inlet and outlet channel emerging into the fluid chamber, wherein the fluid chamber has a cross section that broadens out relative to the inlet channel in the direction of flow from the inlet to the outlet channel and is designed, thanks to the broadened cross section, to broaden a first liquid volume that is essentially pressure-driven and conducted through the inlet channel and through the fluid chamber to a cross section at least approximately corresponding to the full cross section of the fluid chamber, while the fluid chamber has a holding position and is configured so that a second liquid volume, placed in the fluid chamber through the feed opening, can be held in the region of the holding position and the second liquid volume when the first liquid volume is moved through by pressure can be taken up by the latter and delivered as a combined liquid volume through the fluid chamber and into the outlet channel.