Inflammatory periodontal diseases are related to dental plaque formation. Increase in the perfusion of the inflamed tissue results in increased oxygen supply. Although oxygen has healing effects, it is bound to be a mediator of peroxidation in biological membranes. Chemotherapeutic agents such as chlorhexidine, listerine, sanguinarine, and cetylpridinium chloride and oral antibiotics such as tetracycline HCl and doxycyline were tested for their antioxidative activities. While doxycyline has the highest antioxidant activity in lower volumes (0.1 ml), sanguinarine, listerine and a pace after them, tetracycline HCl, had similar effects in higher volumes (0.3 and 0.4 ml). The results showed that in addition to their antiseptic or antimicrobial effects, these preparations have an antioxidative activity against spontaneous oxidation.