['Cutaneous T-cell lymphoma (CTCL) comprises a spectrum of presentations, including erythroderma, pruritus, lymphadenopathy, and circulating atypical lymphocytes. Photopheresis is an extracorporeal treatment in which white blood cell concentrates are subjected to UV irradiation when the serum methoxypsoralen level is above 50 ng/mL. Of patients with CTCL, those with erythroderma have been most responsive to this therapy. In some conditions, including certain malignant hematologic neoplasms, serum soluble interleukin 2 receptor levels (SIL2R) correlate with disease activity. We sought to determine whether serum SIL2R levels correlated with disease activity in six erythrodermic patients with CTCL treated primarily with photopheresis. We measured SIL2R levels in five patients with stage III or greater erythrodermic CTCL and one with stage IIa CTCL. We compared SIL2R values with clinical course, skin scores, CD4/CD8 ratios, peripheral white blood cell counts, and Sézary cell counts, using Pearson correlation coefficients.', 'The SIL2R levels correlated with clinical course and skin scores, even when controlled for other factors noted above.'] Do serum soluble interleukin 2 receptor levels in erythrodermic cutaneous T-cell lymphoma correlate with response to photopheresis-based treatment?