Abstract: The present invention provides a method of identifying an agent which modulates an activity of a protein, wherein the protein is represented by the amino acid sequence of SEQ ID NO: 1 or has at least 90% amino acid sequence identity to SEQ ID NO: 1 and transports chloride ions across a cell membrane, comprising: (a) exposing cells which express the protein to the agent; and (b) measuring degree of chloride ion transport in the exposed cells, wherein a change in the degree of chloride ion transport compared to control cells, which express the protein but not exposed to the agent, is indicative of an agent capable of modulating an activity of the protein. The agents identified by this method can be used for the prevention or treatment of various diseases caused by the dysfunction of calcium activated chloride channel.