Patients with nonerosive gastroesophageal reflux disease often have relatively low esophageal acid exposure and respond suboptimally to gastric acid suppression. In these patients, other constituents of gastric contents may induce esophageal symptoms. We have demonstrated that gastric contents can cause heartburn when the gastric pH >4. (Aliment Pharm Ther 14:129-134, 2000). The aim of this study was to determine relative sensitivities to chenodeoxycholic and ursodeoxycholic acids, and 0.1 N HCl, administered as provocative perfusion tests. Patients with functional heartburn and healthy control subjects were evaluated. Patients underwent a modified Bernstein acid infusion test and esophageal Barostat balloon distention. Time and volume to pain were recorded. Barostat balloon distention was performed using our standard protocol. Stepwise distentions were performed and pain was recorded. Sensitivity to chenodeoxycholic acid (Cheno) and Ursodeoxycholic acid (Urso) were assessed similarly to the Bernstein test using 2 mM concentrations of each, followed immediately by 5 mM if no pain was reported with 2 mM. Volume of bile acid infusion and length of time until pain was induced were assessed and compared to the same endpoints for acid sensitivity. "Total" time and "total" volume to induce pain were calculated for Cheno and Urso. Least-squares means were generated and two-tailed t-tests and regression analyses were performed (P < 0.05 level of significance). Ten functional heartburn patients and six healthy controls were evaluated (3 M, 13 F; age range, 19 to 56 years). Since five of six controls had pain with acid infusion (hypersensitive), all subjects were analyzed as one group. Only three subjects (all controls) had no pain with infusion of 2 mM Cheno and received the follow-up infusion of 5 mM. These same three subjects tolerated the maximum infusion (150 ml and 15 min) of 5 mM Cheno. Nine subjects did not have pain with 2 mM Urso and received the follow-up infusion of 5 mM Urso (five functional heartburn, four controls). Significantly more subjects tolerated the maximum bile acid infusion of 2 mM Urso vs 2 mM Cheno (nine vs three; P < 0.05, Chi-square test). The pain threshold (volume and time) for Urso was significantly higher than that for Cheno and acid (P < 0.05), and the pain threshold for Cheno was significantly higher than that for acid (P < 0.05). Conclusions are as follows: (1) Bile acids differ in their ability to induce pain. (2) Changing bile acid composition by treatment with Urso may change symptom presentation and symptom severity in patients with bile acid-induced esophageal pain.