This study is concerned with the effects of aluminium, arsenic, boron, cobalt, copper, fluorine, iron, iodine, lithium, magnesium, molybdenum, and zinc onBacillus thuringiensisvar.thuringiensisBerliner. Addition of small quantities of the elements to the culture medium stimulated growth of theBacillus. The effect was particularly marked during cell division, as revealed by an increase in area of the clones. The toxic effects of certain concentrations of the elements was also revealed during cell division, which, as indicated by the clonal area, was adversely affected by B, Cu, I, Mg, and Zn. F, Fe, Li, and Mo effected retardation of the cell division by as much as 12 to 48 hours. Al, As, Cu, and Mg both retarded and reduced cell division. By determining the relation between the effective limiting doses established, we were able to divide the elements into four groups. The toxicity of the elements was also revealed by its effects on the germination of the spores, clonal structure, form of the cells, time of sporulation, synthesis of the toxin-crystal, and cellular lysis.