The concentration of nitrite and N-nitroso compounds was examined in the fasting gastric juice of 44 patients with regard to the known cancer risk of the operated stomach. All patients had been operated for ulcer disease in average 2.5 years previously. Twenty-six age-matched individuals with healthy stomachs figures as a control group. The concentration of nitrite and N-nitroso compounds in the gastric juice of the vagotomized patients (PGV) did not differ from that of the controls. On the other hand, a significant increase of the nitrite concentration was found in gastric juice of patients resected according to Billroth I or II procedure. The fraction of N-nitroso compounds, however, was significantly elevated in comparison to the other gastric juice samples only in the Billroth II-resected stomach. The importance of the increase of nitrite and N-nitroso compounds for the cancer risk inherent to the gastric stump is discussed.