Abstract: A device for particle counting includes a metering device for metering a volume of a liquid sample containing particles and a cylinder for dosing a volume of a diluting liquid to a dilution chamber. The cylinder has first and second ends and a piston. A conduit connects a first end of the cylinder and the dilution chamber. The metering device introduces the liquid sample in the conduit and movement of the piston towards the first end displaces diluting liquid and sample to the dilution chamber which communicates with the second end of the cylinder and is preferably located therein, whereby movement of the piston towards the second end causes pressurizing of the dilution chamber to displace diluted sample from the dilution chamber through a particle counter. The piston has a piston rod extending through the first cylinder end, whereby movement of the piston towards the first end causes an increase in volume (V.sub.2) in the cylinder on the second piston side that is greater than the decrease in volume (V.sub.