This work presents an experimental study of the reaction mixture hydrodynamics along the industrial unit for epsilon-caprolactam polymerisation by determining the mean residence time and dispersion criterion. The residence time distribution functions were obtained from radiotracer measurements. Different flow types for different zones of the industrial polymerisation unit have been evidenced: plug-flow with small mixing in the reactor feeding pipe and stirred flow with flow defects (stagnant zones and short-circuits) for the polymerisation column. These results were used for the optimisation of the operating regime of the epsilon-caprolactam polymerisation unit.