The dietary toxicity of four Bacillus thuringiensis insecticidal proteins (CrylA(b), @IA(c), CryIIA, and CryIDA) was evaluated against two Gollembola species. Folsomia candida (Willern) (Isotomidae) and Xenylla grisea AxeIsora (Hypogastruridae). Test diets were prepared by adding the respective purified B. thuringiensis proteins to aqueous suspensions of Bakers yeast (Sacchamnyces cerevisiae) and lyophilizing the mixtures to obtain final test concentrations of 200 pg B. thuringienis protein per gram of diet. Collembola were tested inside petri dish microcosms containing a moistened 9: 1 plaster of paris: charcoal mix. The numbers of surviving adults and progeny were recorded following 21 days exposure to the test diets. None of tie B. thuringiensis proteins significantly reduced Collembola survival or reproduction compared to the negative yeast control. The insecticide chlorpyrifos was used as a positive control for assay validation. Chlorpyrifos significantly reduced F. candida adult survival and reproduction at diet concentrations > 20 ug g-l; X. grisea was not significantly affected by chlorpyrifos concentrations up to 200 pg g-1. The test results demonstrate that the relatively low concentrations of B. thuringiensis insecticidal proteins present in the tissues of transgenic crop plants do not pose a toxicological risk to soil Collembola.