In this paper an analysis of the effects on the steady-state operation of PI-controlled CSTRs induced by noise in the temperature measurement is discussed, both numerically and theoretically. The theoretical approach was carried out in a simplified way, by solving the Fokker-Planck equation of the linearisation of the stochastic model of the reactor at the stable steady state. The effectiveness of this simplification is discussed : the linearisation is a valid approximation for controlled CSTRs, apart from a narrow region near the Hopf bifurcation. Linearisation has subsequently been applied for the identification of reliable safety criteria for the choice of the control gains, with the advantage of a major saving of time. Stochastic resonance is also analysed. (C) 1998 Elsevier Science Ltd. All rights reserved.