The ability to consume complement and activate neutrophils was investigated for staphylococci adherent to silicone surfaces and non-adherent staphylococci. Staphylococcus epidermidis strain ATCC 14990 and Staphylococcus aureus strain E 2371 were used in this study. The bacteria were allowed to adhere to silicone catheter segments for 2 h at 37 degrees C. Complement consumption was measured by reduction in serum haemolytic activity against sheep red blood cells. The induction of chemiluminescence was measured after opsonization of the staphylococci in 20% AB-positive human serum for 60 min at 37 degrees C. The bacteria consumed complement to approximately the same extent when adherent to the catheter segments, but more slowly in comparison with planktonic bacteria. When planktonic bacteria were compared, complement was consumed more quickly by S. epidermidis than by S. aureus. Measuring the induction of chemiluminescence by planktonic bacteria, S. epidermidis induced a lower response than S. aureus, while when adherent to the catheter segments the bacteria induced similar responses. These responses were only 15 to 20% of those induced by planktonic bacteria and only slightly higher than the spontaneous chemiluminescence by the neutrophils. Inter-strain variation was found, but all strains induced about the same low chemiluminescence when adherent to the catheter segments. The reduction in inflammatory response caused by adherence of staphylococci to catheter segments may interfere with phagocytosis and elimination of S. epidermidis during the early establishment of a foreign body infection.