Mutants of the bacteriophage lambda have been isolated which can form plaques as well as transduce a series of bacterial loci. Included amongst the loci carried by the phages are the chlA genes which control membrane components involved in the nitrate respiration complex of E. coli. By using the appropriate chlA deletion mutants and λpchlA phage, it was possible to transduce control of formic dehydrogenase activity with the chlA genetic locus.