A dilution apparatus suitable for use with particles suspended in a fluid is described. The apparatus comprises a first batch diluter and a second continuous diluter. The first diluter comprises a vessel having at least one inlet, and an outlet, the at least one inlet being arranged to receive diluent so as to mix said sample with said diluent. The second diluter comprises a sample input, a diluent inlet and an output, the diluent input being arranged such that diluent entering the second diluter experiences a pressure drop. The pressure drop is sufficient to entrain at least a portion of diluted sample from the first diluter through the sample input. The outlet of the first diluter is arranged to be in communication with the input of the second diluter such that a sample that has been pre-diluted in the first diluter is arranged to be further diluted in the second diluter.