Although the physiological levels of LPS are said to be 10–15 ng l−1, and little or none of it is free , in our hands the addition of LPS at these concentrations caused immediate coagulation when they were added to WB. Figure 2 shows the effect of 0.2 ng l−1 O111:B4 LPS when added to WB and incubated for 10 min. Dense matted deposits are spontaneously formed; these are not seen in healthy WB. Fibrinogen with added O111:B4 or O26:B6 LPS with just 30 s exposure (no thrombin added) also spontaneously formed matted deposits (results not shown). Figure 2.Effect of O111:B4 LPS (0.2 ng l−1) on whole blood (without thrombin), where dense matted deposits were spontaneously formed, not seen in control whole blood smears.