Using the signal sequence trap (SST) method we isolated and sequenced the Stromal Derived Receptor-l (SDRl), a new rnouse gene. Two cDNAs clones were detected: a and b (1.9 and 2.4 Kb, respectively). SDRl belongs to the irnrnunoglobulin superfarnily with four cysteines located at highly conserved positions. a and b rnolecules contain a signal peptide, two irnrnunoglobulin-Iike dornains (C2- and V-type), transmernbrane and cytoplasrnic dornains. b forrn has an additional specific dornain encoding an stretch of 116 residues.