A program package KINSIMI for an interactive simulation of homogeneous isothermal reactor systems with an arbitrary elementary kinetics has been developed. The simulation of ideal reactors, tanks-in-series, normal axial dispersion reactors and segregated and maximum mixed tanks-in-series and axial dispersion reactors can be performed with the program package. For the ideal reactors and tanks-in-series both step responses and steady states can be computed. For the axial dispersion, segregation and maximum mixedness models the treatment is limited to a steady state stimulation. For the segregation model, empirical batch reactor kinetics can be used in the computation of continuous reactor performance. The corresponding mathematical models and the numerical algorithms are discussed. Two examples of the application of the package are given. The program package can be used for reactor design as well as for educational purposes in illustrating the influence of different reaction mechanisms and flow patterns on the conversion and product distribution.