The hypothesis of increased oxidative stress in alcohol-dependent patients postulates that altered free radical metabolism is involved in the various symptoms associated with this disease, including brain atrophy, peripheral polyneuropathy, alcoholic liver fibrinogenesis, and cancer. Using an in vivo assay for quantitation of hydroxyl radical (.OH) levels in peripheral blood, we detected increased values in patients suffering from alcohol dependence when compared with non-dependent control persons. The assay used in this study involves the injection of acetylsalicylic acid, which is metabolized in vivo by direct reaction with .OH to 2,3-dihydroxybenzoic acid (DHBA). The time curve for the concentration of the reaction product (2,3-DHBA), determined by high-performance liquid chromatography, thus estimates the .OH radical level in the peripheral blood of individuals undergoing this test. For the first time, we used the intravenous application of acetylsalicylic acid to avoid artifacts arising from differences in gastrointestinal resorption, known to be disturbed in alcoholism. The areas under the 2,3-DHBA time curves differed significantly (p < 0.05) between patients and controls (0.54 +/- 0.27 vs. 0.36 +/- 0.19 microM.h). This study presents further evidence for alterations in radical metabolism in vivo in patients suffering from alcohol dependence. The assay can also be used in further studies dealing with antioxidative treatment (radical scavengers) to evaluate the effectiveness of such therapy.