Abstract A method of inoculation was developed to determine the rate of bacterial development, which consists of printing a standard dilution of microorganisms on a solid medium by means of a special inoculator which allows the growth of 21 isolated clones. Periodical measurement of the margin of clones and microscopic analysis of the degree of development are the criteria used in determining the rate of bacterial development. The method also involves a study of the influence of some oligo elements introduced in the media, on Bacillus thuringiensis var. thuringiensis Berliner. The effectiveness of the method was verified by testing the influence of various trace elements on the rate of development of the bacilli.