Helicobacter pylori is a human gastric pathogen which is extremely well adapted to its unique habitat. Crucial for the survival under the acidic conditions prevailing in the stomach is the enzyme urease. Transcriptome analysis has shown that transcription of a large number of genes responds to the exposure of H. pylori to acid including the genes encoding the urease subunits UreA and UreB as well as several genes which have been previously identified as target genes of the two-component system HP166-HP165. Here, we provide genetic evidence that a stimulus perceived by the histidine kinase HP165 is pH since increased transcription at acidic pH from the promoters controlling the expression of the ORFs hp119 and hp1432 which belong to the HP166-HP165 regulon is strictly dependent on the presence of histidine kinase HP165. Furthermore, we show that the basal transcription from the promoter of the ureA gene is modulated by the HP166-HP165 two-component system in response to acidic pH. On the other hand, the acid-induced increase in transcription of the promoter directing the expression of the orphan response regulator HP1021 is not controlled by the HP166-HP165 two-component system, nor is it mediated by HP1021 itself.