Following evidence for the intoxication of bees, the systemic insecticide imidacloprid was suspected from the mid nineties of having harmful effects. Recently, some studies have demonstrated that imidacloprid is toxic for the bees at sub-lethal doses. These doses are evaluated in the range between 1 and 20 µg kg−1, or less. It appeared thus necessary to study the fate of imidacloprid in the environment at such low levels. Thus, we developed methods for the determination of low amounts, in the µg kg−1 range, of the insecticide imidacloprid in soils, plants and pollens using high pressure liquid chromatography — tandem mass spectrometry (LC/APCI/MS/MS). The extraction and separation methods were performed according to quality assurance criteria, good laboratory practices and the European Community’s criteria applicable to banned substances (directive 96/23 EC). The linear concentration range of application was 1–50 µg kg−1 of imidacloprid, with a relative standard deviation of 2.9% at 1 µg kg−1. The limit of detection and quantification are respectively LOD = 0.1 µg kg−1 and LOQ = 1 µg kg−1 and are suited to the sub-lethal dose range. This technique allows the unambiguous identification and quantification of imidacloprid. The results show the remanence of the insecticide in soils, its ascent into plants during flowering and its bioavailability in pollens.