Seventy-one patients whose duodenal ulcers had healed after a 4-week treatment period with tripotassium dicitrato bismuthate (TDB) were randomly allocated to receive maintenance treatment with either one TDB swallow tablet nocte (equivalent to 120 mg Bi2O3) or an identical placebo. During 12 months of follow-up, no side-effects were reported by TDB-treated patients, blood bismuth levels did not rise above discontinuation threshold concentrations (greater than 50 micrograms/L in the first 6 months, or greater than 100 micrograms/L in the second 6 months), and there were no adverse effects on haematological or biochemical indices. Ulcer relapse was significantly less in TDB-treated patients (P less than 0.025). Cumulative relapse rates at 6 and 12 months were 51% and 66%, respectively, for placebo-treated patients and 26% and 31%, respectively, for those who received TDB. It is likely that TDB is a safe and effective maintenance treatment for patients with duodenal ulcer disease.