Peritoneal lavage is the most valuable diagnostic modality presently available for the evaluation of patients with blunt abdominal trauma. A retrospective review of 523 patients who underwent open peritoneal lavage for blunt abdominal trauma over a 3 1/2-year period revealed serious intra-abdominal pathology in 83% of patients undergoing laparotomy with RBC lavage counts in the range of 20,000 to 100,000 cells/mm3, a level considered by many authors to be negative or indeterminate. Two patients with isolated small bowel perforations had an elevated amylase level as the only measured abnormality. The data indicate that the standard guidelines for RBC positivity (positive count greater than 100,000 cells/mm3 and indeterminate count 50,000 to 100,000 cells/mm3) result in missed intraperitoneal injuries in a large percentage of patients and therefore require reevaluation. Lavage amylase determinations, previously stated to be costly and of insignificant yield, should be performed on patients whose lavage would otherwise be considered negative by RBC and WBC counts.