The persistence of the insecticidal protein of Bacillus thuringiensis (Bt) is enhanced by the reactivity with soil particles and may constitute a hazard to the soil ecosystem; however, studies on the fate of the Bt toxin in soil, especially in the presence of inorganic salts, are limited. The effects of different concentrations of KNO3, KH2PO4 and NH4H2PO4 on the adsorption of Bacillus thuringiensis toxin by kaolinite, montmorillonite, goethite and silicon dioxide were investigated. Results showed that small salt concentrations tended to enhance toxin adsorption, whereas large concentrations (>10 mmol litre1) inhibited sorption. Similar results were observed regardless of the order in which toxin and inorganic salt were added. The degree to which individual salts affected adsorption decreased in the sequence for minerals, goethite>kaolinite montmorillonite>silicon dioxide, and for ions, H2PO4>NO3, NH4>K.Our results indicate that inorganic salts can markedly influence the adsorption of Bt toxin by soil minerals. This investigation will help in evaluating the behaviour and fate of Bt toxins in the soil environment.