The purpose of the study was to define duodenal epithelial function in duodenal diseases and to assess the potentialities of correction of detected dysfunctions. The electrical properties (EPs) of the duodenal epithelium were explored in patients with primary chronic duodenitis, duodenal peptic ulcer (DPU) on an exacerbation and in the late postoperative period after selective proximal vagotomy. Mucosal biopsy specimens were obtained at fibrogastroduodenoscopy with biopsy forceps and placed in a sign-alternating field with the parameters, adequate bioelectric epitheliocytic characteristics: 28 V at a voltage sign change rate of 1 Hz, and a current strength of 200 microA. Bioelectrical cell reactions (nuclear fluctuation amplitude) were recorded by light microscopy using a MOB-1A ocular micrometer at minutes 10, 30, and 60 of the onset of electrical field action. A significant reduction was found in the amplitude of duodenal epithelial nuclear fluctuations in the examinees, which was most pronounced in DPU on an exacerbation. Duodenal epithelial EPs were shown to undergo regular changes during therapy and may serve as an additional test in evaluating the efficiency of therapy.