Previous studies on the medical use of ozone therapies show a very diverse array of results, from ozone reducing the amount of HIV virus in the blood, to no effect, to causing the death of several patients due to pulmonary embolism and infections. However, ozone therapies are widely used in Europe and considered medically safe. In the U.S., doctors in 28 states use ozone therapies. The objectives of this study were to investigate the effects of medical grade ozone at varying concentrations used in ozone therapies. These were achieved by evaluating the C-reactive protein, erythrocyte sedimentation rate, total reduced and oxidized glutathione content of erythrocytes which were all markers used to determine ozone injury/inflammation. Despite the fact that ozone is a very strong oxidant, previous research indicates that depending on the dose and the health status of the biological system, sometimes ozone can act as an antioxidant. The medical exposure range for ozone is between 20-80 mg/ml with an average of 50 mg/ml. The concentrations used in this study were 20, 40, 80 and 160 mg/ml. Ozone was generated in the "Breath Lab" at USF from medical grade oxygen obtained through electrical corona arc discharge using an OL80C ozone generator. De-identified blood samples of 10 ml blood/sample containing EDTA as anticoagulant were obtained from the James A. Haley VA Hospital patients. Equal volumes of blood and ozone gas mixture were allowed to mix in ozone-resistant syringes prior to dividing each sample into three parts, one for each corresponding parameter to be studied. The C-reactive protein was analyzed through ELISA using the colorimetric method available from Helica Biosystems; erythrocyte sedimentation rate was measured in graduated sedimentation tubes; the total reduced glutathione (GSH) and oxidized glutathione (GSSG) content of erythrocytes was determined according to the colorimetric method developed by the Oxford Biomedical Research. Overall, the concentrations of ozone used did not have a statistically significant effect on the parameters investigated. However, a small percentage of the blood samples showed an improvement in the parameters studied, especially at the highest ozone concentration.