Angiotensin II subtype 1 (AT1) receptor cDNA was cloned by expression cloning from bovine adrenal cortical cells. Human AT1 receptor was also cloned. These receptors were found to have a seven transmembrane structure. The receptor seems to interact with more than one type of G-proteins. AT1 consists of subtypes. cDNA for AT1A was cloned from rat kidney and that for AT1B was cloned from rat adrenal by plaque hybridization. They have similar base sequences in the coding region but are different in non-coding regions. Their functional implication is not clear. The regulation of the receptors occur at many stages. Expression of mRNA is studied in cultured rat mesangial cells. It was down regulated by angiotensin II and cAMP. On the other hand in whole body experiments, chronic infusion of angiotensin II was shown to upregulate adrenal AT1, and bilateral nephrectomy or losartan (CAS 124750-99-8) administration reduced AT1 mRNA expression. In addition to AT1 and AT2 the presence of a new subtype AT3 has been shown.