In a prospective randomized trial anterior lesser curve seromyotomy with posterior truncal vagotomy (ASPTV, n = 48) has been compared with proximal gastric vagotomy (PGV, n = 43). Eighty-eight and eighty-three patients were available for follow-up studies at 1 year and 2 years, respectively. Six months postoperatively the mean reduction in pentagastrin-stimulated peak acid output (PAO) was 48.5 per cent (s.d. 26.3) after PGV and 50.5 per cent (s.d. 23.3) after ASPTV. Two years after the operation satisfactory clinical results (Visick I + II) were found in 84.2 per cent of the patients after PGV and in 88.9 per cent after ASPTV. There was a significant difference in the duration of surgery. No serious postoperative gastric sequelae were encountered after either operation. Up till January 1987, eight endoscopically proven, symptomatic recurrent ulcers have been diagnosed: four in the PGV group (9.3 per cent) and four in the ASPTV group (8.7 per cent). The results of this randomized study suggest that ASPTV is as good as PGV in the surgical treatment of chronic duodenal ulcers.