Urinary excretion of pseudouridine, a modified nucleoside, was assessed in 30 patients with Hodgkin's disease, and 106 patients with non-Hodgkin's lymphoma, classified according to the Kiel system. Elevated excretion was found in 47% of 49 patients with high-grade malignant (HGM) lymphoma, and in 37% of 57 with low-grade malignant (LGM) lymphoma, in 13% in Hodgkin's disease, and 3% in 79 reference individuals. The level of pseudouridine excretion correlated with clinical stage in HGM lymphoma (p < 0.0001), but not in LGM lymphoma or Hodgkin's disease (p = 0.086 and 0.36 respectively). Of 28 patients with B-symptoms 71% had elevated excretion, compared to 26% of 108 without B-symptoms (p < 0.0001). Elevated excretion of pseudouridine before therapy was associated with shorter survival time in LGM lymphoma stage II to IV disease, (p = 0.022), and a similar tendency was also observed in HGM lymphoma. Using Cox proportional hazard model, age, malignancy grade, excretion of pseudouridine, and disease stage were identified as independent prognostic factors in non-Hodgkin's lymphoma.