Intra -oral halitosis (bad breath) is reported to affect 15 -83 % of the adult population. Having intra- oral halitosis is a social and psycho- logical handicap, and may cause people in the person’s social circle to increase the physical distance or to turn their faces in another di- rection to avoid the unpleasant smell from the exhaled air. Such be- haviours may affect the individual’s self -confidence resulting in ins e- curity in social and inti mate relations. The oral health -related quality of life status has also been reported to be lower in individuals with halitosis. Approximately 90% of what is considered as bad breath is the result of the degradation of organic substrates (proteins) by an- aerobic bacteria of the oral cavity. Intra -oral halitosis can be as- sessed using both subjective and objective methods to evaluate the subject’s exhaled air. The most common one and the one often r e- ferred to as the ” gold standard”, is the organoleptic scoring system (OLS). OLS is a subjective method evaluating the strength of halit o- sis in exhaled air using a scale from 0- 5. One objective method to assess the presence of volatile sulphur compounds in exhaled air is to use a sulphide monitor measuring the total sum of the volatile sul- phur compounds (T -VSC) in exhaled air. The three gases (hydrogen sulphide (H 2 S), methyl mercaptan (MM) and dimethyl sulphide (DMS)) in exhaled air related to intra- oral halitosis can be assessed separately using a simplified gas chromatograph. Different treatment models such as periodontal treatment, tongue scraping and rinsing with Zn ion containing products have been used to reduce intra -oral halitosis. The present thesis has evaluated the efficacy of different treatment models in t he treatment of intra -oral halitosis.