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A micro flow cell for sandwich immunoassay using Teflon (Asahi Glass Co.: CYTOP/sup TM/) check valves for sample and reagent inlets is designed and fabricated. The check valves are used not only to prevent reverse flow of injected solutions but also to realize sequential injection of the sample and reagent by simple pressure control. The valve structure is designed to control the width and thickness of the sample and reagent flows at relatively small flow velocity that is useful to reduce effective sample and reagent volumes. We examined a fluorescent sandwich immunoassay for human AFP (/spl alpha/-fetoprotein) as a preliminary experiment and faster immunoassay within 30 min compared to the conventional one was realized in the micro flow cell.