The systematic evolution of ligands by exponential enrichment (SELEX™) process is a combinatorial chemistry method for the isolation of nucleic acid ligands (aptamers) that bind to a desired target molecule with high affinity. ln order to increase throughput via automation, we have adapted the SELEX process for protein targets to a robotics-compatible microtiter plate format. A remarkable feature of the platform is that targets are immobilized by hydrophobic adsorption onto the plate surface. Hydrophobic immobilization procedures are simple and require no specialized modification of the protein target. This format was tested by manually performing four independent SELEX experiments. All were concluded within 8 rounds of selection and yielded aptamers that bind in solution to their respective protein target, calf intestinal alkaline phosphatase, human (/.-thrombin or human platelet derived growth factor, with equilibrium dissociation constants below 3 x 10" 10 M.