DAPA is synthesized according the procedure described by Nesheim, et al. (1). HPLC, TLC and spectral analyses are used to determine the purity of the final product. Dansylarginine N-(3-ethyl-1,5-pentanediyl)amide, more commonly referred to as DAPA, is a potent (Ki=10e-7M) and specific synthetic inhibitor of thrombin (1). Of special interest are the unique fluorescent properties contributed by the dansyl moiety of DAPA. When bound to thrombin, the fluorescence intensity and lifetime of the dansyl moiety are increased three fold. The enhancement of fluorescence intensity, coupled with its inhibitory properties, have made this compound extremely useful for studies involving thrombin generation (2-7). In addition to an increase in fluorescence intensity and lifetime, there is a decrease in depolarization of the excitation signal which also supports fluorescence polarization studies. The inhibitor properties of DAPA alone have been useful in a variety of applications. DAPA is routinely used