End products of nucleic acid metabolism including beta-aminoisobutyrate (beta-AIB) and pseudouridine (psi-Urd) have been considered as potential biochemical markers for cancer. The urinary excretion of both metabolites was investigated in abnormal hematopoietic conditions including 26 patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) and was compared to that of 25 healthy controls. beta-AIB excretion in CML was directly correlated to the leukocyte count, the indicator of tumor cell mass. beta-AIB excretion was elevated in 27 and 75% of untreated AML and CML cases, respectively. Marrow blast cell content tended to correlate positively with psi-Urd excretion in AML. psi-Urd excretion was elevated in 82 and 87% of untreated AML and CML, respectively. Turnover of hematopoietic cells seemed to be a determinant for beta-AIB excretion, indicating higher cell turnover in CML patients compared to that in AML patients and in controls. With cytostatic treatment, excretion levels of beta-AIB and/or psi-Urd decreased after a transient rise.