A novel, simple and rapid stability-indicating spectrofluorimetric method has been developed for the determination of valacyclovir hydrochloride in tablets and spiked plasma samples. Method based on the reaction between valacyclovir and fluorescamine in borate buffer solution of pH 9.0 to give highly fluorescent derivatives that were measured at 475 nm using an excitation wavelength of 390 nm. The method has linear relation with fluorescence intensity in the concentration range of 0.25-1.25 mu g/mL. The developed spectrofluorimetric method was validated with respect to linearity, precision, sensitivity, accuracy and selectivity. The degradation behavior of the drug was also investigated: the drug solution was subjected to neutral, acid and alkali hydrolysis, oxidation, thermal stress and exposure to the sunlight. The method proved to be selective and useful for the investigation of the stability of valacyclovir. Successful applications of the developed method for the drug determination in tablets and spiked plasma samples were also performed.