A field site equipped with suction lysimeters was installed at Treviglio (BG) to assess the migration capacity of the herbicides terbuthylazine, alachlor, metolachlor, linuron and monolinuron and to verifity the appearance of their relevant transformation products. Two different hydrological situations were simulated: a constant hydraulic head was applied to reach the interstitial water saturation in the surficial soil layer or an intermittent pluviometric condition was generated. The results showed two main processes of transport: in the first one transport was mainly due to water infiltration through macropores; in the second one it was driven by matrix flow. Metolachlor and monolinuron resulted to be the most mobile herbicides, while desethyl-terbuthylazine and chloroanilines were found to be the major transformation products.