The invention provides an apparatus and method for conducting chemical or biochemical reactions on a solid surface within an enclosed chamber. The invention may be used in conducting hybridization reactions, as of biopolymers such as DNA, RNA, oligonucleotides, peptides, polypeptides, proteins, antibodies, and the like. In another aspect, the invention provides an improved method for mixing a thin film of solution, as in a hybridization chamber. The invention further provides a kit for carrying out the methods of the invention.