13 C. diphtheriae strains were used as a model to establish the conditions of making the fingerprint analysis of chromosomal DNA. These strains, subdivided into 7 groups in accordance with the character of their restriction splitting, were mostly isolated from territorially close sources and belonged to the same phagotype. Probably, C. diphtheriae DNA has strain variations manifested by an unequal number and location of the sites of the recognition of specific endonucleases, which may be used for the intraspecific differentiation of C. diphtheriae.