On-line concentration measurements from an isothermal semi-batch system, i.e. the liquidphase acetoacetylation of pyrrole with diketene, are used for identification of a kinetic model. An integrated expert system, containing coupled estimation procedures and statistical analysis tools as well as a kinetic model data bank, chooses the most suitable structure for the kinetic model and subsequently identifies model parameters. With the increased availability of data during the run, refinements or structural changes in the kinetic model are performed automatically and parameter estimates are updated. A recently developed short-cut procedure (the Modified Integral transformation Procedure, MIP, Maria and Rippin, 1995, 1996; Maria, 1995), is compared against classical direct methods. Interactive use of a kinetic model-data bank through a numerical transfer of information strategy allows adaption of the mechanism-based kinetic model structure. Multiple nonlinear state estimators of the Extended Kalman Filter (EKF) type are operated in parallel, while the MIP/kinetic data-bank provides information for switching between the EKFs and concerning mechanism and model structure. This on-line use of parallel direct (short-cut) estimation procedures is particularly suitable for real-time process supervision, control and optimisation purposes.