Severe septic states in humans are responsible for intense intravascular oxidative stress, which induces numerous adaptive mechanisms. We determined time sequence changes in total plasma antioxidant capacity (TAC) and major plasma antioxidant concentrations, which have not been fully explained in septic conditions. A cohort of 56 consecutive septic patients (septic shock n = 37, severe sepsis n = 19) and six healthy volunteers. We compared TAC and antioxidant levels in patients with one of two degrees of septic states, at the onset of illness, to those of healthy volunteers. Thereafter, over a 10-day follow-up, we observed daily the time sequence changes of the two septic populations in terms of TAC and antioxidants. At the onset, there was no difference between the three groups in terms of TAC values (healthy subjects 2.18 +/- 0.04; severe sepsis 2.03 +/- 0.07; septic shock 2.09 +/- 0.09), then an equivalent time decline was observed in the two septic populations whatever the severity. TAC was statistically linked to uric acid, proteins in particular albumin and bilirubin (multivariate analysis), but no correlation was found with any vitamin (A, C and E). A sharp and persistent decrease in vitamin C concentrations was underlined. TAC, unaffected at first, deteriorated over time whatever the severity of the infection in these critically ill patients. TAC, unable to distinguish severe sepsis and septic shock, is unlikely to be a particularly useful outcome measure.