Abstract: The invention provides a system and method for synthesizing chemicals onto supports in a parallel manner to produce a combinatorial collection of compounds. The system includes a plurality of middle plates, with each middle plate defining a plurality of reaction zones arranged in a two dimensional array. The reaction zones are adapted to receive a solid support, such as a sheet of membrane, and the middle plates are stackable on each other to form a three dimensional array of reaction zones. The system also includes a pair of end plates, where the middle plates are located between the end plates, and where the end plates include an array of fluid guides corresponding to the array of reaction zones, to allow for selective routing of reagents through the reaction zones.