This study aimed to investigate the persistence of imidacloprid in soil after application to cotton seeds and to obtain a complete picture on the mass balance of this compound in soil and cotton plants. The study was carried out as a pot culture experiment under laboratory conditions using a Gaucho formulation containing (14)C-labeled imidacloprid. Three treatments of cotton seeds were made in sandy loamy soil: live seeds grown in autoclaved soil, dead seeds put in live soil and live seeds grown in live soil. Results showed that total (14)C recoveries decreased by time ranging 93.8-96.2, 77.1-88.4 and 53.5-62.4% of the applied radioactivity at 7, 14, and 21 d after application, respectively. The reduction in the extracted (14)C from soil coincided with the increase of non-extracted ones. Levels of bound (14)C was always less in autoclaved soil than in live ones. Results revealed also that only 1.8-6.8% of the applied (14)C was taken up by the plants and fluctuated within the test period. (14)C levels were higher in plants grown in autoclaved soil than those in live ones and the radioactivity tended to accumulate on the edges of cotton leaves. Most of the radioactivity in the soil extracts was identified as unchanged (14)C-imidacloprid.