For special purposes a combination of methods is described which allows to determine salicylic acid (including acetylsalicylic acid) and its main metabolites in blood plasma and urine separately and quantitatively. Salicylic acid (SA) and salicyluric acid (SU) are extracted from the acidified fluid with ether and afterwards reextracted in an aqueous phase. By fluorometry at different wavelengths, it is possible to differentiate between SA and SU. The conjugates of SA and SU are hydrolyzed with sulfuric acid and then extracted in the form of SA and SU. The four analyses (SA, SU and their conjugates) are of satisfying accuracy and sensitivity. To test the validity of the method in vivo, the concentrations of SA and its conjugates were determined in the plasma and urines of healthy volunteers. By a simplified, but nevertheless accurate, modification of the described method total salicylate in the urine can be determined.