Transaldolase (TAL) is a key enzyme of the pentose phosphate pathway (PPP). TAL deficiency is a newly recognized cause of liver cirrhosis. We have developed an ion-pair LC separation combined with negative ion electrospray MS/MS detection method to assess PPP metabolites in urine samples from TAL-deficient mice. Sedoheptulose 7-phosphate (S7P), C5-polyols D-arabitol and D-ribitol, and 6-phosphogluconate (6PG) levels were markedly increased in urine of TALdeficient mice with respect to those of wild-type and heterozygote littermates. The detection limits of S7P, D-arabitol, and 6PG were 0.15 ± 0.015 pmol, 3.5 ± 0.41 pmol, and 0.61 ± 0.055 pmol, respectively. The limit of quantitation was 0.4 ± 0.024 nmol/ml for S7P, 1.6 ± 0.11 nmol/ml for 6PG and 10 ± 0.7 nmol/ml for D-arabitol. Additional metabolites,