This study investigated the efficacy of a 0.1% chlorhexidine preparation as an aid to a basic oral hygiene programme comprising only baseline root and crown debridement, instruction in bass brushing without emphasis on interdental cleaning, and pulsated mono-jet subgingival irrigation. Baseline data for plaque index, papilla bleeding index and probeable pocket depth were similar in both test and control groups. Mean values for all 3 parameters were clearly lower in the chlorhexidine group, both at the end of the period of active treatment and up to 2 months thereafter. These differences were statistically significant for P1I at day 28, PBI at day 56 and PPD at days 56 and 84, but not at day 168. Proportionately more sites generally showed improvement in the chlorhexidine group at all times. It was concluded that 0.1% chlorhexidine significantly enhances the effects of the practical oral hygiene regime described.