Experimental gingivitis was inducedin 2 groups of 10 adult Wistar rats by feeding them a high sucrose diet for 30 days. Since cyclosporin has an immunosuppressive effect on the stimulation of T lymphocytes, the test group received 5 intraperitoneal injections of cyclosporin A from day 20 to 30 while the control group received no additional treatment. The gingival regions of the molars were studied in light and transmission electron microscopy. In both groups, a well‐differentiated wall of polymorphonuclear neutrophils (PMNs) was present between the dental plaque and the papillary epithelium and no bacterial invasion occurred despite the local absence of T lymphocytes in the test group. It can be concluded that T lymphocytes are not involved in the mechanism of bacterial invasion.J Periodontol 1993; 64:24–28.