About biological nitrogen fixation most information on the genetic and enzymatic level is known from investigations with Klebsiella pneumoniae. The gene region for N2-fixation (nif) was transferred from K.pneumoniae to the enterobacterium Escherichia coli. After acquisition of nif E.coli is able to fix nitrogen. Plasmid pRD1 was constructed which carries the nif-region. Using genetic engineering techniques the exact location of nif on pRD1 was determined. Subsequently the nif-region comprising 7 operons with 14 known genes was cloned on a multicopy plasmid vector. The use of the Klebsiella-nif-region in biotechnology is discussed. Difficulties arising in experiments designed to construct N2-fixing plants are mentioned.