Biosynthetic processing of the T-cell surface receptor for interleukin-2 was investigated in a cultured human T-cell line MT-1 by means of metabolic and cell surface radiolabeling followed by immunoprecipitation with a monoclonal anti-receptor antibody (anti-Tac) and analysis by one- and two-dimensional polyacrylamide gel electrophoresis. The nascent precursor of the receptor (Mr = about 40,000, pI = 6.2-6.5) underwent a post-translational modification giving rise to the mature receptor (IL-2R; Mr = 60,000-65,000, pI = 4.2-4.7) within 2-4 hr. The post-translational processing of IL-2R caused a 20,000-25,000 increase in apparent molecular weight and a 2.0-2.5 acidic shift in the isoelectric point. The increase in molecular weight was attributable mainly to addition of sugar residues including glucosamine and galactose, and the charge shift to the addition of sialic acids. A carboxylic ionophore monensin completely blocked the maturation of IL-2R at the mid-stage of the processing. Fatty acid attachment appeared to comprise one of the steps of the post-translational modification. Two-dimensional analyses of IL-2R biosynthesis enabled identification of the precursor of IL-2R and its intermediate forms, from which it was partially possible to estimate reactions involved in the maturation of the precursor molecule.