Abstract: The present invention pertains to a process for determining an analyte, especially a low-molecular-weight pollutant in a sample. It is carried out by partially dipping into the sample a test strip, on which antibodies which are specific for the analyte and to which in turn a tracer is bound, are immobilized. During the capillary migration of the sample through the test strip, the analyte partially displaces the tracer. The tracer that has remained on the antibody is subsequently visualized by, e.g., dyeing. The intensity of the dyeing is an indicator of the amount of analyte detected.