Adherence of polymorphonuclear leukocytes (PMNLs) to nylon in patients with bacteremia was studied using a whole-blood assay. Adherence of PMNLs was studied in blood obtained from patients who were not in shock; the results did not differ from the control values (70.9% +/- 4.9% vs 72.1% +/- 2.8%, respectively; P greater than 0.3). Adherence of PMNLs in the whole blood of patients was studied 24-36 hr after antibiotic therapy was begun for documented bacteremia, and elevated values were demonstrated (79.2% +/- 8.6%; P less than 0.01). patients with bacteremic shock had a greatly augmented level of PMNL adherence (91.1% +/- 8.5%; P less than 0.001), and enhanced adherence was demonstrated when the normal PMNLs were suspended in plasma from hypotensive patients. The administration of methylprednisolone significantly reduced the adherence of PMNLs in the whole blood of four patients with bacteremia. Assay of PMNL adherence to nylon is a simple test with the potential of identifying bacteremic patients who are at risk of developing shock.