['Interleukin-6 (IL-6) is a potent immunomodulatory cytokine that may have pathogenetic and prognostic significance in a number of disorders. The objective of this study was to examine the correlation between serum IL-6 levels and phenotypic characteristics, as well as outcome of patients with diffuse large-cell lymphoma (DLCL).', 'Using an enzyme-linked immunosorbent assay (ELISA; lower limit of sensitivity, 0.35 pg/mL), we measured IL-6 levels in frozen sera from 33 healthy controls and 58 untreated patients with DLCL who were enrolled onto a single combination chemotherapy protocol. Serum IL-6 levels were correlated with clinical and laboratory features at diagnosis and with failure-free and overall survival.', 'Serum IL-6 levels in the lymphoma patients (median, 4.37 pg/mL; range, < 0.35 to 110 pg/mL) were significantly higher than in the control group (median, < 0.35 pg/mL; range, < 0.35 to 1.87 pg/mL) (P < .0001). Serum IL-6 levels were higher in patients with B symptoms (P = .012), an elevated beta 2-microglobulin level (> or = 3.0 mg/L) (P = .017), and a poor performance status (P = .02). Direct linear correlations with the erythrocyte sedimentation rate (ESR), platelet count, and total WBC count, and an inverse linear correlation with the serum albumin level, were observed (all P < .02). Patients with elevated serum IL-6 levels had inferior failure-free (P = .042) and overall survival (P = .05) compared with those with normal serum IL-6 levels.'] Do serum interleukin-6 levels correlate with prognosis in diffuse large-cell lymphoma?