There is disclosed a device for multiparallel synthesis or screening of a chemical library that includes at least one, and preferably more than one, plate with a two-dimensional or three-dimensional array of wells. Openings are provided in the side walls between at least some of the wells, through which the fluid can flow between adjacent wells. At least one inlet for each plate is provided whereby fluids can be introduced into the array of wells in each plate and flow between adjacent wells in each of the plates through the openings in the side walls.