This study compared a simplified oral hygiene regime (scaling, root planing and Bass brushing) with this same regime plus 0.02% chlorhexidine (CH), 0.05% metronidazole (MD) and inactive control (PL) solutions delivered supragingivally by a pulsating water jet irrigator. 22 patients were distributed randomly into 3 groups, 0.02% chlorhexidine (CH), 0.05% metronidazole (MD), and inactive control (PL). Approximal surfaces with associated pockets greater than or equal to 4 mm were monitored at day 0, for plaque index (PII), gingival index (GI), sulcus bleeding index (SBI), baseline measurement for gingival shrinkage and probable pocket depth. All monitored surfaces were then immediately scaled and root planed. All patients received identical oral hygiene instruction (Bass brushing), with a sodium fluoride toothpaste and a multituft toothbrush, and were shown how to use the oral irrigator. Proficiency in use of the oral irrigator was checked again at day 7. No interdental cleaning was taught. The active treatment period was 28 days. Patients were seen at days 7, 28, 56 and 84, and all parameters were recorded at each visit, but no further oral hygiene instruction was given. Within procedure comparisons of the findings at days 28 (end of active treatment) 56 and 84 with those at day 0, showed statistically highly significant improvements in all parameters for all groups. Regarding between procedure comparisons, CH was better in reducing PII at all times except at day 84, and on several occasions in reducing GI and SBI. Irrigated groups were always better than nonirrigated groups. Although the differences were statistically highly significant, clinically the differences between groups were relatively small, except for CH effect on PII.(ABSTRACT TRUNCATED AT 250 WORDS)