Carbonic anhydrase II (CA2), is one of fourteen forms of human alpha Carbonic anhydrases. Carbonic anhydrases (CAs) are a family of zinc metalloenzymes. Using Southern blot analysis and restriction endonucleases, it is determined that the CA2 gene consists of 7 exons. Using a mouse CA II cDNA hybridization probe with a panel of mouse-human cell hybrids, The CA2 gene was assigned to human chromosome 8. CA2 is expressed at high levels in osteoclasts during bone resorption. It is demonstrated in 2 in vitro culture systems that antisense RNA and DNA blocked expression of CA2 and led to decreased bone resorption. In the choroid plexus, CA2 supports the transport of bicarbonate ions, sodium ions, and water from the blood to the cerebrospinal fluid.