We present a rapid and convenient method to perform and evaluate the covalent protein binding of reactive phase I metabolites. The oxidative metabolism of the drugs paracetamol, amodiaquine, and clozapine is simulated in an electrochemical (EC) flow-through cell, which is coupled online to an LC/MS system. Adduct formation of the reactive metabolites with the proteins beta-lactoglobulin A and human serum albumin proceeds in a reaction coil between EC cell and injection system of the HPLC system. The formed drug-protein adducts are characterized with online time-of-flight mass spectrometry, and the modification site is localized using FTICR-mass spectrometry. Due to its simple setup, easy handling, and short analysis times, the method provides an interesting tool for the rapid risk assessment of covalent protein binding as well as for the synthesis of covalent drug-protein adducts in high purity and high yield.