Interpretations of tracer tests involve matching field data by the use of computer simulation programs. As the complexity of the simulator model increases, the number of trial runs needed to fit field data satisfactorily increases rapidly. The conventional fitting procedure can thus become cumbersome and can involve prohibitive computer costs. This study presents a new methodology that is devised to model tests in heterogeneous formations. These rigorous simulators written in high-level computer languages are replaced by simple response functions generated in spreadsheet software. Matching the tracer data now involves function evaluations rather than full simulator runs, resulting in a large reduction in computing time. Analyzing laboratory tracer tests shows the uses of spreadsheet models. Advantages and disadvantages of the technique are discussed. (C) 2001 Elsevier Science Ltd. All rights reserved.