Polaprezinc, an insoluble zinc complex of L-carnosine, exhibits anti-ulcer effects by acting directly on mucosal lesions. The disposition of polaprezinc in the stomach was studied to clarify the usefulness of its structure as an insoluble complex. The time courses of ¹⁴C-radioactivity in the gastric contents and gastric tissues were parallel to those of ⁶⁵Zn after oral administration of a mixture of ¹⁴-Cpolaprezinc and ⁶⁵Zn-polaprezinc (¹⁴C-, ⁶⁵Zn-polaprezinc) to rats. The gastric contents of ¹⁴C-polaprezinc and ⁶⁵Zn-polaprezinc were greater than those of ¹⁴C-L-carnosine and ⁶⁵ZnSO₄. Mean residence times (MRT) of ¹⁴C-polaprezinc and ⁶⁵Zn-polaprezinc in the stomach were almost the same (ca. 2 hr), and they were double those of ¹⁴C-L-carnosine and ⁶⁵ZnSO₄. In gastric tissues, the area under the concentration curves (AUC_{0-8 hr}) of ¹⁴C-polaprezinc and ⁶⁵Zn-polaprezinc were 1.7 times greater than those of ¹⁴C-L-carnosine and ⁶⁵ZnSO₄, respectively. After administration of ¹⁴C-, ⁶⁵Zn-polaprezinc to rats with acetic acid-induced ulcers, ¹⁴C and ⁶⁵Zn-radioactivities in the ulcerous sites were very similar and greater than those of ¹⁴C-, ⁶⁵Zn-polaprezinc dissolved in acid. In conclusion, polaprezinc is retained in the stomach longer and adheres to the ulcerous sites more than zinc or L-carnosine. The characteristics of this compound may arise from its insolubility and contribute to its strong pharmacological action.