Postoperative sepsis remains a major problem in current surgical practice. This study assesses the predictive role of neutrophil chemotaxis in the development of sepsis in surgical patients. Neutrophil chemotaxis was measured in 30 cancer patients undergoing gastrointestinal surgery and in 26 healthy age and sex-matched controls. Neutrophil chemotaxis was significantly reduced (P less than 0.02) in the patients (mean 79.2 micron +/- 2.7 s.e.m.) compared with the controls (mean 86.8 micron +/- 1.9 s.e.m.). In the entire patient group neutrophil chemotaxis did not change to any appreciable extent following surgery. However, in the seven patients who developed postoperative septic complications, chemotaxis, which was similar to control levels in the pre-operative stage, declined significantly following surgery. Pre-operative values for the septic group of patients are 92.4 micron +/- 4.02 s.e.m.. These declined to 73.4 micron +/- 3.15 s.e.m. (P less than 0.05) and to 68.2 micron +/- 2.89 s.e.m. (P less than 0.05), 5-8 days (early) and 10-14 days (late) postoperatively respectively. Neutrophil chemotaxis in the non-septic group of patients did not alter over this same period. The data suggest that the onset of postoperative sepsis in patients is accompanied by impairment of chemotactic properties in their neutrophils. However, it is also evident that measurement of this variable in patients before operation does not help to define an 'at risk' group for the development of postoperative sepsis.