The technique of nucleic acid hybridization, in which target and probe strands of DNA or RNA are duplexed as a means of identifying the target, has the potential to become one of the most widely used ways of identifying pathogenic virus and bacteria. Unfortunately, inconvenient methods of detecting hybrids have restricted the technique primarily to research laboratories. Among the many different detection methods that are currently being researched, one especially simple approach seems to have been largely overlooked. This is direct gravimetric determination using a quartz crystal microbalance (QCMB), which is sensitive in the nanogram region. This proposal is aimed at testing the feasibility of detecting hybrids at a solution-crystal interface as they form. A one-year project is planned. A simple flow cell will be constructed. A crystal mounted in the cell will have probe immobilized on its surface. Synthetic RNAs will be used as model targets and probes. Target Will be injected and the signal will be observed in real time. A detection limit goal of 10 ng is proposed. The method is labelless in the sense that no reporting labels are needed. Goals of project include determination of detection limit, sensitivity, and reaction rates.