An effect was studied of electromagnetic radiation of the millimetric wave band (EHF EMR) on ultrastructural processes of the mucosa and healing of ulcer in 10 patients with duodenal ulcer. Biopsy specimens were taken from the base of the margin of the ulcer and in the area 1 cm from the margin of the ulcer defect before the treatment, after 5 and 10 sessions of EHF EMR to acupuncture points. EHF EMR was found to exert a stimulating effect on the processes of ulcer regeneration. Seen after session 5 are layers of proliferating poorly differentiated enterocytes, activation of immune and autoimmune processes, normalization of the hemomicrovessel endothelial cell structure, filling in the ulcer defect with a newly formed granulation tissue in which, among fibroblasts, macrophages, mast cells and lymphocytes, there prevail plasmic cells with an augmented secretion of immunoglobulins, increase in proliferation of epitheliocytes, with their differentiation slowing down, and a complete epithelialization of the ulcer following ten treatment procedures.