We describe an in vivo cloning method using mini-Mu phage for genes, which cannot be cloned on multicopy vectors, mainly for their toxicity. We have successfully cloned succinate dehydrogenase (sdh) gene E. coli which was inactivated with defined insertion of fragment Kmr by this method. The most of obtained Kmr clones of mini-Mu transductants have contained the sequence of whole sdh gene. The intact gene of sdh can be reconstructed by site-directed mutagenesis.