Octopamine and synephrine are endogenous biogenic, and hydrophilic, amines. Both compounds are used as alternative to ephedrine. Synephrine is also used as fat loss drug. Both compounds are very similar in nature. Analytical HPLC method based on a mixed-mode HPLC approach, using a Primesep 200 column, was developed to separate octopamine and synephrine with LC/MS compatible conditions. Octopamine and synephrine are retained by combination of reversed-phase and cation-exchange mechanisms. Method can be used for analysis of both substances in biological fluids (blood, serum, urine). Monitoring can be done by UV, LC/MS, ELSD, CAD, etc.