The present paper reports on the behaviour of a pseudo first-order reaction system in a batchwise operated stirred tank reactor. The experimental results refer to runaways, sensitive and stable operations and are compared with two different runaway criteria, i.e. the Semenov criterion and the Adler and Enig criterion. These criteria present the minimum heat-transfer capacity beta(c) required for a safe design of a reacting system for a given adiabatic temperature rise alpha and a given ratio epsilon of the Arrhenius temperature and the modified coolant temperature. It is shown that : - the Semenov criterion is conservative but safe, - the Adler and Enig criterion holds at low values of alpha, while at high alpha values runaways already occur before beta(c) is reached. For constant values of alpha and epsilon, the measured sensitivities of operating curves at beta values in the vicinity of beta(c)are compared with normalized objective sensitivities S-beta of Morbidelli and Varma.