Imidacloprid (1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitro-1H-imidazol-2-amine, 1) is a new insecticide which is useful for the protection of sugar beet from soil insects (Atomaria, Blaniulus, Agriotes and Pegomya) and leaf insects (aphids). It is applied in pelleted seed dressing. It is a systemic compound which is absorbed by the plant. In the leaves, it gives a long lasting (3 to 4 months) protection against aphids and the virus yellows infections. The metabolism of 14C-imidacloprid was investigated in plant cell suspension cultures (Koester 1992). The main metabolites corresponded to imidacloprid hydroxylation (l-[(6-chloro-3-pyridinyl)methyl]-5-hydroxy-4,5-dihydro-N-nitro-lH-imidazol-2-amine) or dehydrogenation (1-[(6-chloro-3-pyridinyl)methyl] -N-nitro-lH-imidazol-2-amine) of the imidazolidine ring, and to 6-chloronicotinic acid. The nitroso derivative of imidacloprid (1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nitroso-1H-imidazol-2-amine) corresponded to only 0.1% of the total recovered 14C. The imidacloprid soil metabolism has been studied by incubation in laboratory conditions (Scholz and Spiteller 1992). The metabolites observed in plant cell cultures did not accumulate in soil; their total amount was less than 4% of the total recovered radioactivity during 14C-imidacloprid soil biodegradation. 14CO2 was the main product of 14C-imidacloprid soil biodegradation. We previously studied the disappearance of imidacloprid in the soil of a sugar beet, organic fertilizers trial made at Lubbeek in 1992 (Rouchaud et al. 1994). Also, in a sugar beet trial located at Remicourt, one part of the field had not been treated with organic fertilizers for 18 years, but its soil contained a high concentration (4.3%) of soil organic matter. Another part of the field had been treated every 3 years with cow manure for 18 years, but its soil contained a normal concentration (2.4%) of organic matter. In the present work, we studied the imidacloprid soil metabolism in a new organic fertilizers trial made on another field at Lubbeek in 1993. We also searched for the imidacloprid soil metabolites in the trial made in 1992 at Remicourt.