The cell surface receptor for interleukin 2 plays a central role in the biology of this T-cell growth factor. A combination of affinity chromatography, high-performance liquid chromatography, and NH2-terminal protein sequencing was used to purify and chemically characterize the interleukin 2 receptor both from phytohemagglutinin-activated T cells and from the human T-cell lymphoma cell line HuT-102. The receptor isolated from HuT-102 cells was purified 16,000-fold to homogeneity as evidenced by (i) a final specific activity close to the theoretical specific activity of 18,182 fmol of receptor per microgram of protein, (ii) a single band on polyacrylamide gel electrophoresis with an Mr of 55,000, and (iii) a unique, unambiguous NH2-terminal protein sequence. The receptor purified from phytohemagglutinin-activated T lymphocytes had an Mr of 60,000 but it had the same NH2-terminal protein sequence.