We have previously demonstrated an increase in lymphocyte function associated antigen-1 (LFA-1) expression in the native intestines of animals with graft versus host disease (GVHD) after small bowel transplantation (SBTx). The present study evaluated LFA-1 expression on peripheral blood lymphocytes (PBLs) during GVHD. GVHD was created in LBNF1 rats by heterotopic vascularized SBTx from Lewis donors and compared to sham-op controls and cyclosporine-treated SBTx rats (SBTx-CyA, 10 mg/kg/day). PBLs were harvested on Postop Day 13 when signs of severe GVHD were present and PBLs were stained for LFA-1, CD3 (T-cell marker), and CD45 (B cell marker) and analyzed on an Epics 5 flow cytometer. Mesenteric lymph node (MLN) lymphocytes from the native intestines were also harvested for each group and stained for LFA-1. There were significant decreases in LFA-1, CD3, and CD45 PBL expression in rats with GVHD. CyA treatment corrected the abnormal CD3 and CD45 ratios, but not LFA-1 expression. It is concluded that: (1) The proportion of PBLs expressing LFA-1 is depressed in animals with clinical GVHD consistent with their recruitment into the host's inflamed tissues. (2) CyA treatment corrects the abnormalities in T and B cell ratios but not the decreased expression of LFA-1 on PBLs and may relate to its known imperfect ability to treat GVHD.