Serum pepsinogen (SP) behavior was evaluated under basal conditions and under betazole stimulation in 59 patients: 14 controls, nine unoperated duodenal ulcers (DU) and 36 DU after proximal gastric vagotomy (PGV), 14 with and 22 without recurrent ulcer. The mean follow-up of the 36 patients who underwent PGV was 38.7 months. SP was higher in unoperated DU than in the control group (p less than 0.05). After PGV in DU, there is a significant decrease of SP for both the patients with and without recurrent ulcer (p less than 0.05), being statistically similar to the control group. No difference of SP was observed between DU with and without recurrent ulcer after PGV. We concluded that SP can differentiate normal subjects from DU patients, although it is not a sensitive indicator of recurrent ulcer after PGV.