Previous studies showed that either the urease activity possessed by H. pylori and the bacterial load may influence the results of the [13C] urea breath test. However, the correlation between urease activity and dyspepsia is unclear. The aim of our study was to evaluate whether the urease activity of the gastroduodenal tract may influence the severity of dyspeptic symptoms. In all, 2520 dyspeptic patients (1109 men, 1411 women; mean age 47 +/- 16 years) without gastroesophageal reflux disease, diabetes, vascular disorders, liver and biliary tract diseases, and tumors of the gastrointestinal tract and with a normal appearing abdominal ultrasonography were enrolled. All these patients underwent a [13C] urea breath test and filled out a questionnaire on dyspeptic symptoms. Subjects were divided in five different groups according to delta over baseline (DOB) values (group 1 < 3.5, group 2 = 3.5-6; group 3 = 6.1-11, group 4 = 11.1-23, group 5 > 23.1). The prevalence and intensity of dyspeptic symptoms were compared among groups. In all, 1688 patients (67%, 928 females and 760 males; mean age 48 +/- 15 years) were H. pylori-positive. The chi-squared test and analysis of variance showed increase of frequency and intensity of each dyspeptic symptom according to DOB values. In conclusion, Dyspepsia may parallel gastric urease activity. However, whether higher DOB values are related to higher bacterial load or, alternatively, to the presence of particular H. pylori strains able to produce larger amounts of urease is uncertain.