The metabolic profiling of biological fluids is important in understanding the various biochemical processes in the human body. The content of aromatic metabolites, including microbial ones, in the blood and cerebrospinal fluid, can provide essential information reflecting infectious processes, both systemic and in the central nervous system. A sensitive method with protein precipitation and sample concentration using ultra-high-pressure liquid chromatography-tandem mass spectrometry was proposed and subsequently validated to determine the number of aromatic metabolites of phenylalanine, tyrosine, and tryptophan in the blood serum and cerebrospinal fluid at 2.0-3.7 × 10