Anoctamin 1 (ANO1) protein has been identified as the Ca²⁺ activated Cl^- channel. In epithelial tissues ANO1 is widely expressed and has a clear function in epithelial cells of airways and intestine, as well as salivary and pancreas glands. Apart from ANO1, other members of the ANO family are expressed in these organs. In the present study we therefore analyzed expression of all ten members (ANO1- ANO10) in a broad range of murine tissues and detected predominant expression of ANO 1, 6, 7, 8, 9, 10 in epithelial tissues, while ANO 2, 3, 4, 5 are frequent in neuronal and muscle tissues. When expressed in Fisher Rat Thyroid (FTR) cells, all examined ANO proteins could be detected by immunocytochemistry. However, only ANO 1, 2, 6 and 7 produced Ca²⁺ activated Cl^- conductance, as analyzed by ATP-induced iodide quenching of YFP fluorescence. In contrast ANO9 and ANO10 suppressed baseline Cl^- conductance and coexpression of ANO9 with ANO1 inhibited ANO1 activity. Patch clamping of ANO-expressing FRT cells indicated that apart from ANO1 also ANO10 produced Ca2+ activated whole cell currents, albeit with different Ca²⁺ sensitivity and activation time course. We conclude that ANO proteins form Ca²⁺ dependent Cl^- channels with variable regulatory properties. This study is supported by SFB 699 A/7 and EU-FP6-2005-CH-037365.