An automated system of reactors carries out a solid-phase peptide synthesis, and more particularly a solid-phase peptide synthesizer which is automated, by means of a reactor with a liquid-recirculation loop making it possible to measure, in real time, chemical species in the reactor via measuring cells. This system includes inlet pipes, namely: pipes dedicated to the introduction of resin, pipes dedicated to the introduction of the synthesis and washing solvent, pipes dedicated to the introduction of the agent for deprotecting the amino acid introduced, pipes dedicated to the introduction of the reagents, and includes an assembly reactor and a loop for recirculation of the liquid of the reactor.