The role of gastrin in the pathogenesis of recurrent peptic ulceration is not established although it is known that plasma gastrin levels are frequently elevated after vagotomy. This study aims to determine whether there is a relationship between gastrin and gastric secretion in patients with and without recurrent ulceration after surgery for duodenal ulceration (DU). The basal acid output (BAO) in 23 and the peak acid output to pentagastrin (PAOPg) in 10 patients with symptomatic recurrent ulcers after DU surgery were determined along with the BAO and PAOPg in 10 control patients who were asymptomatic following DU surgery. The fasting plasma gastrin was determined in all patients and correlated with the acid output. An inverse correlation was demonstrated between the BAO and plasma gastrin in the asymptomatic patients (p less than 0.05) and the patients with proven recurrent ulcers (p less than 0.01) and there was a direct correlation between the PAOPg and plasma gastrin in the recurrent ulcer group (p less than 0.05) which was not observed in the control group. It is suggested that in a subgroup of recurrent ulcer patients 'G cell hyperfunction' may occur and this may have a role in the aetiology of this condition.