a multi - well assay plate structure and assay apparatus and a method for performing chemical biochemical assays is described . the multi - well assay plate structure defines a relatively shallow substantially enclosed space above a plurality of wells , with the enclosed space having an inlet and an outlet separate from the inlet . fluid introduced via the inlet flows into the space and / or wells by displacing air . withdrawal of the fluid via the inlet or outlet leaves fluid in the wells allowing various tests to be performed . various embodiments of the structure are described . the preferred arrangement embodies the structure on a transparent plastic disk which can be used with automatic fluid handling apparatus and the results assessed using optical assessment apparatus . the apparatus can be used to perform a variety of assays but , in particular , biochemical / chemical assay , immunoassays and genetic assays and it can be used in a laboratory for multiple sample testing or at a point - of - care , i . e . in a surgery or clinic .