This study was conducted to evaluate whether vitamin C (VC) was associated with total antioxidant status (TAS) in human plasma and to determine the usefulness of VC on TAS in the treatment of patients with paraquat poisoning. VC and TAS were measured in 56 healthy subjects. Then, various concentrations (1-100 mg/dl) of VC in pooled plasma from 10 volunteers were constructed in vitro and TAS was measured. The VC and TAS were measured in vivo at 0.5, 1, 2, 3, 5, 7, 9, and 11 h after injection of VC (50 mg/kg) in seven volunteers and pharmacokinetic data were calculated. Finally, various amounts of VC (100, 500, 1000, 3000 mg/day, and 3000 mg/8 h) were given to 10 paraquat-poisoned patients for 5 consecutive days, and blood was taken for TAS 1 h after each injection. The means (SD) of VC and TAS in healthy subjects were 2.22 (0.16) mmol/l and 0.48 (0.10) mg/dl, respectively. Positive correlation between VC and TAS was observed in both in vitro and in healthy volunteers. The pharmacokinetic results in vivo were as follows: means (SD) of distribution volume, area under curve, plasma clearance, half life, C(max), and T(max) were 32.0 (4.4) l, 36.4 (11.3) mg h/dl, 2.13 (1.36) l/h, 10.2 (7.8) h, 17.1 (7.1) mg/dl, and 0.64 (0.24) h, respectively. Estimated loading and maintenance doses of VC were 2278 mg and 146 mg/h, respectively. The means of TAS were increased over 5 consecutive days as 2.26, 2.76, 2.81, 3.18, and 3.58 mmol/l in paraquat patients. All patients were recovered within mean (SD) 21.2 (5.4) admission days. Our data suggested that VC was a significant antioxidant as TAS in human plasma and that increased TAS by high doses of VC could be useful as a free radical scavenger for paraquat poisoned patients.