The invention relates to a method and an apparatus for performing an assay on chemical, biochemical, or biological fluids. The apparatus includes an assay chamber for fluid reactions and a centrifugal force activated-valve for controlling fluid movement through the assay chamber. An active surface can be positioned in the assay chamber to react with fluids passed through the assay chamber. The active surface may contain biomolecular probes. The biomolecular probes can be DNA, DNA fragments, RNA, RNA fragments, reagents, protein, protein fragments, lipids, and lipid fragments. The apparatus is particularly useful when multiple reactions, dilutions, or washing steps are required to determine a final answer. The centrifugal force activated-valve provides positive control over fluid in the assay chamber and allows for repeated use of the same chamber for multiple reaction steps. The apparatus can be disposed of after an assay to eliminate potential contamination from reuse of the same apparatus. Fluids passed through the assay chamber may be recovered for subsequent analysis, processing, or reactions.