BACKGROUND/AIM L-Ascorbic acid (AA) is the predominant circulating form of vitamin C found in human blood. It has been hypothesized that surgical stress increases the vitamin C metabolite dehydroascorbic acid (DHAA). Vitamin C is mainly excreted through the kidneys. In this study, the ratio of AA to DHAA excreted in urine was determined in patients who had undergone total hip joint endoprosthesis surgery (n = 12), and the results were compared with data obtained from healthy controls (n = 12). METHODS All subjects received 1,000 mg sodium ascorbate intravenously three times a day (every 8 h) for 8 days, starting 2 days prior to surgery. Total urine was collected daily while subsequent determinations of AA and DHAA were performed photometrically. RESULTS Administration of vitamin C led to average daily excretions of the combined products AA + DHAA of 2,343 +/- 438 mg/day (mean value +/- confidence intervals). The initial average ratio DHAA/AA of all 24 probands was 0.064 (6% DHAA; 153 +/- 76 mg/day). One day after surgery, an increase in the DHAA/AA ratio to 0.165 (15% DHAA; 332 +/- 107 mg/day) was measured in the patients. The ratio decreased 2 days after surgery and returned to normal within 5 days. CONCLUSION Our data indicate that surgery increases the oxidation of AA and urinary excretion of DHAA, as a result of the enhanced formation of free radicals.