The equilibrium absorption and binding of the active toxin from B. thuringiensis, toxic to lepidopteran larvae, to humic acids extracted from two forest and two cultivar soils, as well as the insecticidal activity and the biodegradation of the bound toxin, were studied.  The results of these studies indicate that the toxins from B. thuringiensis introduced in transgenic plants and microbes could persist, accumulate, and remain insecticidal in soil as a result of binding to humic acids, as well as on clays.  This persistence could pose a hazard to non-target organisms and enhance the selection of toxin-resistant target species.