This pilot study compared the effectiveness of subgingival irrigation with 0.12% chlorhexidine, 1.64% stannous fluoride, and sterile saline, in addition to scaling and root planing, on levels of Bacteroides porphyromonas and the clinical parameters bleeding tendency, probing depth, and attachment level. A convenience sample of eight patients, exhibiting 32 sites with moderate periodontal disease, was randomly assigned to receive all treatments according to a four-quadrant treatment design. Subgingival irrigation was performed at 0, 1, 2, and 3 weeks following scaling and root planing. Clinical and microbial assessments were measured at baseline, 4, 8, and 12 weeks. Data were analyzed using a two-factor repeated measure analysis of variance, and the Newman-Keuls sequential range test or Friedman test and Kruskal-Wallis test revealed statistically significant (p less than .01) improvements in probing depths, attachment levels, and Bacteroides porphyromonas for all groups at 12 weeks when compared to baseline values. No statistically significant differences occurred between any of the treatment groups at any time period. Based on the findings of this investigation, it has been concluded that four weekly irrigations with 0.12% chlorhexidine, 1.64% stannous fluoride, or saline irrigation did not enhance the beneficial effects of scaling and root planing alone.