In patients with gastrointestinal hemorrhage, delayed or late scans with Tc-99m labeled red blood cells are readily performed and have prognostic impact when early images are negative. Nevertheless, there have been no indicators for the likelihood of detecting bleeding on such images. In a review of all gastrointestinal bleeding scans over an 8-year period, 73 patients had delayed images >> 3 hours) following early negative exams. For these patients, determinations of serum blood urea nitrogen (BUN) and creatinine (Cr) were evaluated as the BUN/Cr ratio and were compared against delayed scan findings and confirmed diagnoses. Patients with significant renal failure were excluded from analysis. There were 34 late positive (46%) and 39 late negative (54%) studies. Mean BUN/Cr was 26.5 and 20.0 in patients with late positive and late negative scans, respectively (p < 0.05). Occurrence of late positive scans was 38% (19/50) for BUN/Cr < 25.0 vs. 65% (15/23) for BUN/Cr>> 25.0 (p < 0.05). Patients with early negative images and a BUN/Cr ratio of 25 or greater have a greater likelihood of a positive delayed image. Late imaging should be encouraged in patients with elevated BUN/Cr and early negative scintigraphy.