In this work, a solid-state spectrofluorimetric method for drug assays was developed. In particular, we report the determination of salicylic acid (SA), as a hydrolysis product, in solid pharmaceutical formulations containing acetylsalicylic acid (ASA). Recently, we described a sensitive and accurate fluorescence method that provided, through a mathematical application, the simultaneous determination of ASA and SA. By means of the spectrofluorimetric method reported herein it was possible to carry out the SA determination, without any mathematical calculation and with a sensitivity 100 times that of our previous method. The intra- and inter-day reproducibility of the spectrofluorimetric method, expressed as the relative standard deviation, ranged from 0.1 to 0.3%. The present method requires a fluorescence apparatus with the excitation and detection systems in-line (zero angle). The detection system was not sensitive to the excitation wavelength, but was highly sensitive to emission wavelengths from 350 to 800 nm. The results obtained were compared with those of our previous spectrofluorimetric method, together with those of a high-performance liquid chromatography method and a US Pharmacopeia method. The sensitivity of the method was of the order of 10(-8) g.