We describe assay modules (e.g., assay plates, cartridges, multi-well assay plates, reaction vessels, etc.), processes for their preparation, and method of their use for conducting assays. Reagents may be present in free form or supported on solid phases including the surfaces of compartments (e.g., chambers, channels, flow cells, wells, etc.) in the assay modules or the surface of colloids, beads, or other particulate supports. In particular, dry reagents can be incorporated into the compartments of these assay modules and reconstituted prior to their use in accordance with the assay methods. A desiccant material may be used to maintain and stabilize these reagents in a dry state.