The objective was to establish the relationship between the aspiration of free blood (+ASP) versus diagnostic peritoneal lavage (DPL), abdominal injury severity, hemodynamic instability, and the need for immediate operative intervention. We prospectively compared the significance of +ASP to +DPL in our level I trauma center. Consecutive patients received sequential needle tap, catheter aspiration (ASP), and DPL. If gross blood was withdrawn during the tap or ASP, it was returned to the peritoneal cavity before completing the DPL. The DPL was considered positive if there were > 100,000 RBCs for blunt injuries or anterior abdominal stab wounds, or > 10,000 RBCs for other penetrating injuries. During a 12-month period, 566 patients fulfilled the study criteria; they were 50 per cent blunt and 50 per cent penetrating trauma. There were 70 patients with both +ASP/+DPL, 30 with -ASP/+DPL and 4 with +ASP but -DPL. Exploratory laparotomy was performed on these 104 patients (18.4%), 22 of which were considered nontherapeutic. The ATI was statistically higher in the +ASP patients (14.9 +/- 12.9 versus 8.5 +/- 8.2, P < 0.05) but was not clinically different. Overall injury severity and hemodynamic stability were not different in the two groups. The sensitivity of DPL at detecting intra-abdominal injury was higher than the ASP group (98% versus 72%), but the specificities were equal (98%). Because +ASP patients are not more critically injured or unstable than +DPL patients, and because DPL is more accurate in detecting the need for operative intervention, aspiration should be abandoned as part of the DPL procedure in patients with abdominal trauma.