This study describes a method aimed at measuring the bacterial ATP content of dental plaques formed on a polyester support attached on tooth surfaces in the oral cavity. It reports on the variations in ATP content in 3 days old plaques of a well-defined surfaces with or without the use of 0.2% chlorhexidine mouth-wash twice daily. The results, expressed in bacterial equivalents, show a reduction of dental plaque metabolism after 3 days of chlorhexidine rinses to 19.5% of its value in the control tests without mouth-washes. Bacterial metabolism represented 6.05 bacterial equivalents per mm2 in the control group versus 1.18 equivalents in the chlorhexidine test group.