Recombinant human interleukin-2 (rH IL-2, Ser^(125)-rH IL-2) was purified to apparent homogeneity from E. coli in high yield and characterized its biochemical properties for the establishment of preclinical screening system and therapeutic applications. The purification was carried out by methods involving isolation of inclusion body, urea extraction, solubilization and gel filtration chromatography. The renaturation of the product was achieved by extensive dialysis against the storage buffer. The purity was confirmed by SDS-PAGE and HPLC. Amino terminal amino acid analysis and partial amino acid sequence analysis showed that the primary structure of the recombinant protein (rH IL-2) was found to be identical with natural IL-2. The purity and the conformation of the rH IL-2 were also confirmed by obtaining crystals of the recombinant protein.