ANR, an analogue of Escherichia coli FNR, has been shown to be necessary for denitrification, arginine deiminase activity and cyanide production of Pseudomonas aeruginosa. Another CRP/FNR-related regulator, DNR, has also been shown to be necessary for denitrification. In this study, we have found that the transcription of the dnr gene is under the control of ANR. When the dnr gene was expressed by tac promoter in an anr mutant, the strain recovered the ability to grow under anaerobic conditions by denitrification. Nitrate, nitrite, nitric oxide and nitrous oxide reducing activities were expressed, and the structural genes for nitrite and nitric oxide reductases were transcribed under anaerobic conditions in the anr mutant strain transformed with the dnr gene. These findings suggest that the expression of the denitrification system is controlled not directly by ANR but indirectly via DNR. The arginine deiminase activity and cyanide production were not regulated by DNR.