 Preliminary studies reported that plasma citrulline concentrations may be a reliable biochemical marker for intestinal dysfunction and absorptive enterocyte mass. The relationship between citrulline concentration and intestinal function has been supported in other studies including those examining rejection in small bowel allografts. Concentrations of citrulline are dramatically reduced in cases of mucosal damage e.g. moderate graft rejection or viral enteritisand strongly correlate inversely with severity on biopsy. Plasma citrulline concentration is lower also in patients with villous atrophy 2413μmolLthan in healthy subjects 4010μmolLand patients with anorexia nervosa 399μmolL.Experimental studies have been carried out also in assessing the value of citrulline as a marker for severity of small bowel epithelial damage from radiation and viral infections. The plasma citrulline was shown to be a simple, non invasive and sensitive essay to monitor and quantify radiation andor chemotherapy induced small bowel damage in mice and humans. Otherwise, the literature on citrulline as a potential marker of intestinal and nutritional integrity is young and consistent data for specific conditions as for HIV enteropathy are missing.We hypothesise that plasma citrulline concentration is a marker of small bowel absorptive integrity and an appropriate surrogate for HIV related enteropathy. 