Computer-implemented method for determining the interaction of one or more chemical active compounds with one or more organisms by means of a computer system comprising at least one substance module, an application module and an organism module, wherein the substance module contains physico-chemical and/or biochemical information on the substance(s) whose behaviour is to be simulated, the organism module comprises physiological and anatomical information which characterizes the organism with which the substance is to interact, the application module comprises information on the location and the time profile of the administration of the substance(s), and the method comprises the following steps: A) selection of at least one substance from the substance module and analysis of its physico-chemical and/or biochemical characteristics, B) selection from the organism module of anatomical and physiological compartments of the organism in question, selected from at least amongst: a) in the case of mammals or insects: the lungs, peripheral organs, blood vessels, preferably arteries and/or veins, or blood fluid; b) in the case of plants: xylem and phloem stream, and root and/or leaf and/or stem, C) description of the compartments in a computing program with regard to the transport processes of the substance from and to the compartments, degradation processes and active processes by mass transportation equations and kinetic reaction equations for describing the process in question, D) description of the transport processes and, if appropriate, the degradation processes of the active compound of the organism, in the computing program by mass transportation equations and kinetic reaction equations, E) combination of the equation systems selected in steps C) and D) and numerical calculation of the resulting system of coupled differential equations, F) determination of the concentration-time curve of the active compound in selected compartments, characterized in that: - a hierarchical model architecture consisting of modules with different functionalities is used for the computing program and comprise at least the substance module, the application module and the organism module, - the modules are interconnected dynamically during the execution time of the program and hierarchically by the computer system, - subsequently, in step E), a system of coupled differential equations is generated automatically by a DEQ generator, which is solved by numeric integration by a numeric solver and - as a result, concentration/time curves of the respective substance(s) in the diverse compartments of the organism in question are provided. A) selection of at least one substance from the substance module and analysis of its physico-chemical and/or biochemical characteristics, B) selection from the organism module of anatomical and physiological compartments of the organism in question, selected from at least amongst: a) in the case of mammals or insects: the lungs, peripheral organs, blood vessels, preferably arteries and/or veins, or blood fluid; b) in the case of plants: xylem and phloem stream, and root and/or leaf and/or stem, C) description of the compartments in a computing program with regard to the transport processes of the substance from and to the compartments, degradation processes and active processes by mass transportation equations and kinetic reaction equations for describing the process in question, D) description of the transport processes and, if appropriate, the degradation processes of the active compound of the organism, in the computing program by mass transportation equations and kinetic reaction equations, E) combination of the equation systems selected in steps C) and D) and numerical calculation of the resulting system of coupled differential equations, F) determination of the concentration-time curve of the active compound in selected compartments, - a hierarchical model architecture consisting of modules with different functionalities is used for the computing program and comprise at least the substance module, the application module and the organism module, - the modules are interconnected dynamically during the execution time of the program and hierarchically by the computer system, - subsequently, in step E), a system of coupled differential equations is generated automatically by a DEQ generator, which is solved by numeric integration by a numeric solver and - as a result, concentration/time curves of the respective substance(s) in the diverse compartments of the organism in question are provided.