After initial scaling, root planing and cleaning of subcontact areas, chronic periodontitis patients received oral hygiene instruction consisting of Bass toothbrushing using a sodium fluoride toothpaste, but without stress on interdental cleaning. They were then assigned to two groups, one of which self-administered 0.2% chlorhexidine solution subgingivally, once daily for 4 weeks, while the other was subjected to subgingival application of acrylic resin strips containing 40% metronidazole once weekly for 4 weeks. Plaque Index, Sulcus Bleeding Index, probeable pocket depth and gingival shrinkage were assessed for this treatment period and for a further 8 weeks. Highly significant improvements compared with baseline values were achieved and maintained to the end of the study. There were no significant differences between the groups at any time, except for Sulcus Bleeding Index which at Days 56 and 84 showed metronidazole to be superior. It was concluded that the regimens selected were equally effective in improving periodontal health over a 3-month period.