Abstract The influence of a PI controller on the dynamic behaviour of a continuous stirred tank reactor (CSTR) where an exothermic reaction takes place has been investigated. The occurrence of chaotic phenomena is singled out by means of both topological features and of sensitivity analysis to initial conditions. The Feigenbaum route to chaos is recognized, since period doubling bifurcation cascades are observed: the universal characteristics of such a “scenario” are well pointed out. The possible destabilizing effect of a PI controller on such nonlinear systems is demonstrated. A parametric analysis in terms of proportional and integral control constants ( k P vs k I) shows how no general guidance can be given in tuning control parameters, within the region where chaotic phenomena may occur.