The time response of a PI-controlled continuous stirred tank reactor (CSTR), where a first order irreversible reaction occurs, is analysed in this paper. The parameters of the PI controller and the saturation of the cooling water temperature flow are used as parameters to show that self-oscillations and chaotic dynamics can appear. The conditions under which self-oscillation occurs are investigated taking into account heat generation, heat removal and the variation of eigenvalues of the linearized system at the equilibrium points, respectively. Also, the appearance of a Silnikov type homoclinic orbit, giving chaotic dynamics, is realised. The existence of a new set of strange attractors with PI control has been verified and the sensitivity to the initial conditions is also analysed. (C) 2003 Elsevier Ltd. All rights reserved.