INTRODUCTION: The enterocyte-specific protein, intestinal fatty acid binding protein (I-FABP), is detectable in serum only after intestinal injury. Previous studies in animals suggest that I-FABP might be a useful marker of intestinal allograft rejection. MATERIALS AND METHODS: I-FABP was repetitively measured in nine intestinal transplant recipients and correlated with findings of surveillance endoscopy. RESULTS: Average interval between I-FABP determination and biopsy was 3.4 days (SD=4.2 days). Average number of rejection episodes per patient totalled 1.6+/-1.2. General linear modeling demonstrated no tendency for increases in serum FABP to precede histologic graft rejection (P=0.263). Restriction of the analysis to I-FABP determinations 1 day before or on the day of biopsy failed to affect these results. Minor increases in I-FABP were often associated with histologically normal grafts, whereas rejection often occurred when I-FABP was not detectable. DISCUSSION: Serum I-FABP levels do not predict clinical intestinal allograft rejection.