Abstract: A multi-well plate and plate holder assembly comprising a multi-well assay plate clamped between an upper plate holder and a lower plate holder to facilitate handling of the plate, and to prevent the plate from warping when liquid samples placed within wells of the multi-well assay plate are stored, analyzed and/or subjected to a reaction or other process, particularly when the samples are subjected to high temperatures. The upper plate holder is releasably engageable with the lower plate holder. Preferably, at least one detent positions and holds the upper plate holder in relation to the lower plate holder.