Ways of accelerating recovery of the mucous membrane immune system in lethally irradiated mice following syngeneic bone marrow transplantation were studied over a 35-day period by quantification of jejunal intraepithelial lymphocytes (IELs) and lamina propria plasma cells. Recovery after a low bone marrow dose allowing 100% animal survival (LBM) was compared with a high (five times minimal) dose (HBM), or a minimal dose augmented with equal numbers of buffy coat cells (LBM + BC) or small gut mucosal lymphocytes (LBM + GL). The maximal decline and subsequent peak repopulation of IELs were: LBM, days 7 through 14, peaking suboptimally by day 28; HBM, day 14, peaking suboptimally but higher than LBM by day 35; LBM + BC, days 11 through 14, peaking at control levels by day 35; and LBM + GL, day 7, peaking at control levels by day 28. The IEL decline was most severe with LBM and HBM treatment and least with LBM + GL. All transplant groups experienced maximal plasma cell decline by day 7. LBM had the most severe depletion, and LBM + GL had the least. Recovery to control levels for the LBM, HBM, LBM + BC and LBM + GL groups occurred by days 28, 21, 21, and 14, respectively. In all instances, greater than 95% of the plasma cells were IgA positive.