The present invention relates to monoclonal antibodies which are distinguished by high selectivity and affinity for metolachlor and which are therefore outstandingly suitable for use in an immunoassay for the rapid and efficient detection of metolachlor. Another aspect of the present invention relates to hybridoma cell lines which produce said monoclonal antibodies and to immunological methods for detecting metolachlor in samples of soil, water or air using said monoclonal antibodies and to the test kits which can be used within the scope of these detection methods.