histologic findings despite the common practice of endoscopic evaluation.Methods: Thirty-nine patients underwent 49 separate upper and/or lower endoscopies for gastrointestinal symptoms.A pathologist blinded to the patients' clinical staging reviewed biopsy slides for the following histologic signs of GVHD: number of apoptotic bodies per high powered field (400x), maximum number of apoptotic bodies per gland, and the percent of glands with apoptotic bodies.All patients had clinical GVHD staging documented weekly during the study period.The maximum reported stage of intestinal GVHD was used 7 days prior to or after the date of the procedure for correlative analysis.The average was used for subjects with multiple measurements.To accommodate this averaging, a weighted least squares logistic regression model was used with weights for each subject equal to the number measurements taken.Results: Endoscopies were performed a median of 58 days (range 22 e 202) post-HSCT.Univariate analysis performed on patients with stages 2-4 clinical gut GVHD showed a statistically significant association with all 3 histologic signs of GVHD found in the colon (Table 1).Although this trend was also seen in the stomach, this association did not reach statistical significance.Patients with a higher assigned clinical stage of gut GVHD at the time of endoscopy were found to have more histologic signs indicative of glandular apoptosis (Table 2).This observation was seen in both the colon and stomach.Conclusions: Our study showed good correlation of clinical gut GVHD stage with histologic findings.Future prospective studies will be needed to determine a more accurate GVHD grading system based on developing clinicopathologic criteria.