We addressed the process of immigration of Bacillus thuringiensis from soil to leaves and its capacity to grow on bean diffusate medium (BDM), a medium designed to simulate the nutrient composition of the phylloplane.Two different B. thuringiensis strains were inoculated into soils, onto seeds or onto lower leaves of bean plants to determine if they were able to disperse to upper leaves under controlled conditions. While B. thuringiensis isolates were commonly recovered from leaves exposed to such inocula, populations were very low (<10 CFU cm(-2) of leaf). In addition, the number of cells of B. thuringiensis recovered decreased with increasing distance from the soil or from the inoculated leaves. Moreover, B. thuringiensis colonies did not grow well on BDM.This indicates that B. thuringiensis disperses poorly from the soil or the seed to the leaves or between leaves of the same plant under controlled conditions. Bacillus thuringiensis apparently has greater nutrient requirements than other bacterial species that are prominent inhabitants of the phylloplane.Finding the mechanisms that favour bacteria colonization on leaves will in turn help to improve the efficacy of biocontrol agents against the target pests.