Control of batch digesters for magnesium bisulphite pulp cooking is considered. The aim of the study is to obtain a systematic, as well as a systemic problem definition for the subsequent design of higher-level control algorithms. The method of analysis was taken from general systems theory; the general scheme of the systems approach has been adapted to the specific control design problem. Following this approach, first, the behaviour of the basic control algorithms was explored by computer simulation. Based on these preliminary results, a systemic representation of the overall control problem was obtained by defining the pulp cooking process and the basic control algorithms together as a system with three inputs and three outputs. Further, the input-output relations of the system were examined by simulation. The final results are given in the form of three diagrams representing the static responses of the object system to the step changes of a single input. The significance of these characteristics is discussed in terms of information needed for the next step of control design. In addition, the diagrams contain some strategic operational hints for better process management on the lower control level.