The concentration of N-nitrosamines was determined in the gastric juice of 170 patients between 6 months and 33 years after operation for ulcer disease, including 38 patients after resection with the Rydygier method (BI-R), 36 after Billroth II method (BII), 35 after truncal vagotomy with pyloroplasty (VP), 41 after highly selective vagotomy (WWW) and 20 after gastroenterostomy (ZZJ). The concentration of N-nitrosamines in the gastric juice was estimated chromatographically. It was confirmed that their concentration in the stomach was the highest after ZZJ and BII resection, lowest after WWW.