Rapid kinetic analyses are essential for biochemical research Important information on the mechanism and regulation of enzymes, the mechanism of interaction between proteins and nucleic acids, and on the binding of signal transduction molecules (i.e., ligands) to receptor proteins can be derived from the use of stopped-flow spectrophotometry. Most enzymes have turnover numbers between 1 and 106 s-1, which implies that the rate constants for the reactions between intermediates will be usually greater than 1 s-1 and that each step will take less than 1 second to occur. In this proposal we will detail the use of rapid stopped-flow spectrophotometry for the investigation of specific biochemical reactions and the development of a Rapid Kinetics Analysis Center that will facilitate its use and be capable of upgrading the instrumentation.