The Potassium Ion Channel kit is a no-wash cell based homogenous assay for high throughput screening measurements of potassium channel activity. Using thallium influx as a surrogate indicator of potassium ion channel activity, the assay is based on the activation of a proprietay fluorescent dye with a high affinity for thallium that reports potassium channel activity with a large fluorogenic signal which is propotional to the number of open potassium channels on the cell. The assay can be performed in a convenient 96-well or 384-well microtiter-plate format and easily adapted to automation without a separation step. Its signal can be read by a fluorescence microplate reader at Ex/Em = 488/525 nm (bottom read).