Recently, besides the known mouse interleukin 2 (IL-2) molecule, six other IL-2 alleles have been found in different mouse strains. In order to study their in vivo and in vitro biological activities large quantities are required. We cloned the corresponding IL-2 cDNAs into a pET7-7/BL21(DE3) bacterial system, a T7-RNA-polymerase-dependent expression vector, producing between 30 to 100 mg of IL-2 per litre of culture. The purification step is based on the resolution properties of the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) technique and the capability of the IL-2 to regain its activity after SDS denaturation. These purified IL-2 molecules supported the growth of an IL-2-dependent cell line, CTL-L2, in a similar way to a commercial mouse IL-2 control. However, RF IL-2 allele, which is also expressed in NOD mice had a relatively lower growth activity in the CTL-L2 assay. These IL-2 molecules can be obtained in a purified form and totally recovered their activity after elimination of the SDS and 2-mercaptoethanol used in the extraction procedure.