A brushtail possum mesenteric lymph node cDNA library was screened with a grey short-tail opossum Clambda probe and four immunoglobulin lambda cDNAs were isolated. Two of the isolated clones (L5 and L10) contained identical framework 4 regions and constant regions (but different variable regions), suggesting that the possum lambda locus is organized as multiple J-C pairs--a feature seen in the opossum and placental mammals. The cloning of the lambda light chain cDNAs signifies the completion of the basic molecular characterization of the brushtail possum immunoglobulin repertoire. The availability of this sequence data will allow extensive analysis of the immune response of the brushtail possum at the molecular level, as well as the development of specific immunological reagents for detection of immunoglobulin molecules at the protein level.