The purpose of this study was to investigate the possible benefits of stannous fluoride dentifrice (SnF2) and once daily chlorhexidine (CH) in the control of chronic periodontitis, following a single course of scaling and root planing. 14 adult patients with pockets 4 mm or deeper received a thorough scaling and root planing, followed by instruction in the irrigation of those pockets with CH. They were given either SnF2-containing or a placebo dentifrice, and a new multituft toothbrush, but no instruction in routine oral hygiene. Plaque Index (PII), Sulcus Bleeding Index (SBI) and pocket depth were recorded prior to scaling on day 0. The same parameters and gingival shrinkage were recorded at weeks 1, 2, 4, 8 and 12. CH irrigation was discontinued at day 28. Both groups showed highly significant improvements in all parameters except gingival shrinkage after 28 days. PII was significantly less at all stages in the SnF2 group. It reached baseline values by day 56 in the placebo and day 84 in the SnF2 group. Periodontitis as assessed by SBI remained reduced significantly below baseline values in both groups at the end of the study. At this time there was no significant difference between the groups as regards SBI. It was concluded that a single course of thorough scaling and root planing followed by once daily subgingival irrigation with CH for 1 month, produced a reduction in periodontitis still apparent 2 months after cessation of irrigation. This regime allows a 3-month interval between oral hygiene visits. SnF2-containing dentifrice had a plaque control effect additional to that produced by the regime but had no effect on periodontitis as assessed by SBI.