an apparatus and method for the automated preparation of treated monolayers of sample material , comprising : a centrifuge having a rotor carrying removable chamber blocks ; sample and reagent dispensers and control systems . first , centrifugal force sediments sample material discretely to form a monolayer onto a receiving surface member on one of the chamber blocks , while the same centrifugal force opens a valve in the chamber block to drain sample material . then , centrifugal force delivers sequentially into discrete chamber blocks discrete treating agents , during which time the sampler material monolayer is held in place on the receiving surface member by centrifugal force . then , each chamber block is drained centrifugally through its already opened valve . each treated sampler material is confined to an individual chamber block . batch and random access delivery of treating agents can be employed . each chamber block includes separate inlets for the sample and treating agents .