In 39 patients with either pelvic or renal cell tumours, the pre-operative urinary excretion ratios of pseudouridine/creatinine (psi:C) and beta-aminoisobutyric acid/creatinine (BAIB:C) were estimated. In 34/39 of the patients (87%), including both types of tumours, psi: C was found to be increased, and in only one patient was the value decreased. Twenty-five of the patients (64%) had a BAIB:C ratio within the normal range. 10 (25%) had increased and 4 (11%) decreased values. In 13 patients the psi:C and BAIB:C ratios from the affected side were compared with the values in urine from the bladder. Twelve of the patients had higher values of psi:C in the urine from the ureter. In seven patients the ureteric BAIB:C ratio was higher than the bladder BAIB:C ratio and in five patients the ureteric BAIB:C ratio was less than the bladder BAIB:C ratio. In only one patient were the values similar. The results indicate that patients with tumours of the upper urinary tract have changed excretion patterns compared with normal subjects and the urinary ratios on the affected side are different from those on the healthy side. The biological tumour markers pseudouridine and beta-aminoisobutyric acid may be helpful in the diagnosis of tumours in the upper urinary tract.