The persistence of CryIAb protein rhizosecreted in soil is important in the assessment of its environmental risk. Here we report that CryIAb protein from transgenic maize does not accumulate at high levels in soils. Levels of CryIAb protein rhizosecreted by three maize transgenic events (BT11, MON810 and 176) were studied in hydroponic cultures and found only in the MON810 and BT11 events but not in event 176 or control plants. Under field conditions, the cryIAb gene and a basal level of CryIAb protein was detected in soils from plots cultivated with transgenic and non-transgenic maize, possibly from Bacillus thuringiensis present in the soils.