Using a newly developed method by HPLC with ultraviolet detection we measured plasma coenzyme Q10 (CoQ10) level in group of 43 children (19 females and 24 males: ages 1 month-9 years) with an acute inflammatory process. The results for coenzyme Q10 were expressed as molar concentration (mumol/l plasma). Our study confirmed that CoQ10 concentration (median--0.8 mumol/l) was independent of sex, and we established which biochemical parameters influence on ubiquinone levels. The results indicate that CoQ10 concentration is connected with leukocytosis, calcium and magnesium levels. These findings suggested that transferin, amylase and serum glutamic transmainase may also determine the CoQ10 plasma levels.