Abstract: Automatic dilution apparatus and method are provided, and are operable in conjunction with automated sample liquid analysis systems to automatically dilute sample liquids as supplied thereby to automated sample liquid analysis apparatus. One embodiment of the dilution apparatus operates to dilute the sample liquids by flowing the sample liquids from the analysis system sample liquid supply conduit, diluting the same, and returning the diluted sample liquids to the supply conduit for flow therethrough to the sample analysis apparatus for sample liquid analysis. Flow of undiluted sample liquids through the supply conduit is prevented attendant operation of the dilution apparatus. A second embodiment of the dilution apparatus operates to remove predetermined volumes of the sample liquids from the supply conduit, and to replace the same with like volumes of a diluent liquid; thereby diluting the sample liquids in the supply conduit for continued flow to the sample liquid analysis apparatus.