An isotope dilution method was developed for the simultaneous quantitation of unlabelled and deuterated kynurenine in urine. After a single iv loading dose of (Indole

ring-

d

5

) -L-tryptophan

urine excreted in the first 3 hours was collected. Two 10 ml samples from the pooled urine

one with a known amount of unlabelled pure kynurenine added

were purified with an extraction procedure and with cation chromatography. Kynurenine was then derivatized with PFP and analysed with GC-MS.

The result showed that the average concentration and the total amount of unlabelled and deuterated kynurenine in the 3 hours urine were significantly decreased in patients with post-hepatitis cirrhosis in comparison with normal subjects

indicating a decrease of tryptophan pyrrolase activity.