Urinary levels of pseudouridine and 1-methyladenosine in patients with leukemia and lymphoma were measured by the inhibition ELISA using monoclonal antibodies to determine the correlation of nucleosides excretion with disease activity. Significantly elevated levels of these nucleosides were detected in patients with all types of disease tested. Seventy-seven percent (46/60) and 62% (37/62) of patients had elevated levels of pseudouridine and 1-methyladenosine above normal mean + 2S.D., respectively, and combination assay of these nucleosides gave higher positive rate (87%; 52/60) than either single assay. The changes of urinary pseudouridine and 1-methyladenosine reflected the disease status of patients in remission or in relapse and the effect of chemotherapy. These results suggest that urinary pseudouridine and 1-methyladenosine might be clinically useful as complementary markers to the monitoring of the disease status of patients with leukemia and lymphoma by hematological examination.