We report the identification of an EST encoding a murine cysteinyl leukotriene (mCysLT) receptor. LTD₄, LTC₄ and LTE₄ but not LTB₄ or various nucleotides activated Ca²⁺-evoked Cl^- currents in mCysLT₁ expressing Xenopus laevis oocytes. The response to LTD₄ was blocked by MK-571, reduced by pretreatment with pertussis toxin (PTX), and was partly dependent on extracellular Ca²⁺. The identified murine CysLT₁ receptor differs from the hCysLT₁ receptor with regard to PTX sensitivity, receptor-mediated Ca²⁺ influx, and antagonist sensitivity.