The bacterium Actinobacillus actinomycetemcomitans is found in large numbers in subgingival plaque and gingival tissues of patients with LJP and PLS. This bacterium too has been found to cause infective bacterial endocarditis in patients at risk. Antibiotic prophylaxis is necessary for at risk patients with LJP and PLS because significant bacteraemia is produced during extensive periodontal instrumentation, extractions and surgery which are required in managing these cases. The current antibiotic regimens recommended by the American Heart Association/Council on Dental Therapeutics are not effective against this bacterium. A two-stage prophylactic approach is advocated, first with tetracycline for two weeks to eliminate the Actinobacillus actinomycetemcomitans, followed by the regimens recommended by the American Heart Association on the day of the dental procedure itself. Tetracycline should not be used concurrently or as a substitute for the recommended regimens by the American Heart Association/Council on Dental Therapeutics.