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Nitrite-cured meat containing 120 mg Na 15 NO 2 /kg was fed to male ferrets ( Mustela putorius furo ). During consumption of the meat, the animals were dosed orally with 0.87 mmol [2- 2 H]proline. All urine was collected throughout the study and analysed for total N -nitrosoproline (NPRO) and isotopic enrichment of NPRO by mass spectrometry. The cured-meat diet increased the urinary excretion of NPRO 14-fold. Isotope analyses indicated that approximately 70% of the NPRO came from the cured meat, the majority of which was analytically unavailable or ‘bound’ NPRO in the meat. A small portion of the excreted NPRO appeared to be formed in the stomach as a result of ingesting the cured meat. A minor amount of the excreted NPRO did not contain any isotopically labelled atoms. The administration of ascorbic acid did not significantly alter NPRO excretion. Animals dosed orally with 11.4 μmol of a peptide in which the N-terminal proline was nitrosated increased their excretion of NPRO by 385 nmol over the following 48 hr. These data indicate that nitrite-cured meat contains bound NPRO which contributes to the total amount of NPRO in the urine.