The IL 2 receptor isolated from the IL 2-dependent CTL-L cell line was subjected to biochemical analysis. Pulse-chase and tunicamycin studies, as well as digestion with the endoglycosidases, Endo-F and Endo-H, of 35S-methionine-labeled IL 2 receptors suggested a single protein precursor of 32,000 (p32) daltons. The p32 precursor was rapidly processed by addition of high-mannose-containing core N-linked sugars to intracytoplasmic precursor intermediates of 38,000 (p38) and 40,000 (p40) daltons, which undergo further processing to yield a mature surface receptor with heterogeneous apparent m.w. of 52,000 to 65,000 (p58). Two-dimensional gel studies indicated that p58 exhibited broad charge heterogeneity between pH 4.6 and 6.3. Endo-F digestions of p58 shifted the isoelectric focus point to a more basic 5.5 to 7.4. This considerable charge heterogeneity is consistent with the possibility that other posttranslational modifications to the mouse IL 2 receptor occur besides addition of complex N-linked glycans. Immunoprecipitations of the IL 2 receptor from surface iodinated cells also revealed an additional band at 110,000 (p110) daltons. IEF vs SDS-PAGE two-dimensional gel studies demonstrated that p110 also had an isoelectric focus point identical to p58. Western blot studies with an anti-IL 2 receptor monoclonal antibody (7D4) demonstrated that p38, p40, p58, and p110 each expressed the epitope recognized by this antibody. Thus, it is likely that p110 is not a unique molecule that coprecipitates with the IL 2 receptor. Western blot analysis of mitogen-stimulated T and B lymphocytes also revealed bands similar to p58 and p110, although these bands had an average apparent m.w. 3000 to 6000 less than those seen for CTL-L cells.