Elevated urinary levels of modified nucleosides, especially pseudourid
ine (PSI), have been observed in patients with a variety of malignant
neoplasms. In this report, the urinary PSI levels were estimated by hi
gh performance liquid chromatography in 93 patients with brain tumours
and in 40 age and sex matched controls. The PSI levels were found to
be excreted in equal amounts in the control and the tumour groups. The
re was no significant difference in PSI when patients with malignant d
iseases were compared with those with benign tumours. Following therap
y, the PSI levels remained unchanged when compared to the controls and
their preoperative values. It is concluded that urinary PSI concentra
tion is not a useful marker for brain tumours.