The determination of metalaxyl, a systemic fungicide which is widely used to fight against tobacco blue mold, is carried out by gas chromatography. This standard method is long and expensive and it is worthwhile replacing it by an immunoenzymatic method of the ELISA type. The results obtained : good reproducibility and good correlation, correspond to the requirement of laboratories which analyse residual pesticides. However this method can only be considered as a screening, because of its lack of specificity, and confirmation by chromatography is recommended in case of doubt.