The antimicrobial activity of two garlic clones' (1: purple and 2: white) crude extracts against oral microbiota was evaluated in vitro (study 1) and in vivo (study 2). Study 1 consisted of the evaluation of minimum inhibitory (MIC) and bactericidal (MBC) concentrations against nine streptococci strains. In study 2, a 2.5% garlic (clone 2) solution was used as a mouthwash in a 5-week study by 30 subjects. Blood agar and Mitis Salivarius Bacitracin agar were inoculated with subjects' saliva to quantify oral microorganisms and mutans streptococci. Study 1 showed MIC ranging from 0.5 to 32.0 mg ml(-1) for clone 2 and from 8 to 64.0 mg ml(-1) for clone 1. MBC ranged from 1.0 to 128.0 mg ml(-1) and from 8.0 to 128.0 mg ml(-1) regarding clones 2 and 1 respectively. Study 2 showed that 2.5% garlic mouthwash solution had good antimicrobial activity against mutans streptococci and oral microorganisms. Maintenance of reduced salivary levels of streptococci was observed after 2 weeks at the end of mouthwash use. Unpleasant taste (100%), halitosis (90%) and nausea (30%) were reported by subjects after the end of the study. It was concluded that the garlic clones have antimicrobial properties in vitro against streptococci and anticariogenic properties against oral microorganism in spite of its adverse effects.