In a previous study, we observed that root debridement was inefficient in eliminating Actinobacillus actinomycetemcomitans from adult periodontitis lesions. The present report describes the effects on A. actinomycetemcomitans of subsequent treatments of 6 patients that had at least 2 separate sites still harboring A. actinomycetemcomitans 6 months following debridement. 1 site or more in each individual was treated with renewed root debridement and at least 1 other site was treated by surgical excision of the gingival tissue. The results indicated that retreatment with either repeated root debridement or with surgical excision of the gingival tissue was not more effective in eliminating A. actinomycetemcomitans than initial debridement. The possible reasons for this limited therapeutic effect on the subgingival presence of A. actinomycetemcomitans are discussed.