Microorganisms are constantly adapting to changes within their environment. The soil dwelling nematode Caenorhabditis elegans encounters a multitude of environmental conditions during its lifetime including hypoxia, UV exposure, temperature fluctuations and starvation. However, living in a soil environment C. elegans will also encounter fluctuations in environmental pH, a condition to which the adaptive response has not been characterised. The aim of this study was to analyse the global transcriptional response to both acid and alkaline conditions, to identify how the nematode adapts to these environments. Caenorhabditis elegans were resistant to pH conditions between pH3-10 over a four-hour period and the environmental pH influenced the expression of genes whose products are involved in cell signalling, metabolism, cuticle biosynthesis and ion/nutrient transport. The majority of genes that were differentially regulated in acid and alkaline environments encoded uncharacterised proteins and represented 33 and 39% of the genes. Post-transcriptional gene silencing of targets did not confer pH sensitivity, which was attributed to remaining transcripts. As a result of alternative splicing, the gene RO1E6.3 encodes two alpha carbonic anhydrases named, CAH-4a and CAH-4b. Biochemical analysis confirmed that CAH-4b, which showed up regulation at the transcriptional level in alkaline conditions (5-fold), was also the most active CA isoform. Crystallisation studies are being performed on CAH-4b to aid in the identification of the protein's biological function.