Pseudomonas aeruginosa has five terminal oxidases for aerobic respiration. Two of them, the bo(3) oxidase (Cyo) and the cyanide-insensitive oxidase (CIO), are quinol oxidases and the other three, the cbb(3)-1 oxidase (Cbb3-1), the cbb(3)-2 oxidase (Cbb3-2) and the aa(3) oxidase (Aa3), are cytochrome c oxidases. The expression pattern of the genes for these terminal oxidases under various growth conditions was investigated by using lacZ transcriptional fusions and some novel regulatory issues were found. The Aa3 genes were induced under starvation conditions. The Cyo genes were induced by exposure to the nitric oxide-generating reagent S-nitrosoglutathione. The CIO genes were induced by exposure to sodium nitroprusside as well as cyanide. The stationary phase sigma factor RpoS was found to be involved in the expression of the Aa3 and CIO genes. The role of two redox-responsive transcriptional regulators, ANR and RoxSR, was investigated using the anr and roxSR mutant strains. The ANR was involved in the repression of the CIO genes and induction of the Cbb3-2 genes. The other three terminal oxidase genes were not significantly regulated by ANR. On the other hand, all five terminal oxidase genes were shown to be directly or indirectly regulated by RoxSR. The Aa3 genes were repressed but the genes for the other four enzymes were induced by RoxSR. The transcriptome data also showed that some respiration-related genes were regulated by RoxSR, suggesting that this two-component regulatory system plays an important role in the regulation of respiration in P. aeruginosa.