The essential oil concentrations decrease substantially in broth and agar media, when incubated under open conditions. This decrease is caused primarily by evaporation and adherence on plastic surfaces (28). For these reasons, broth dilution assays must be carried out under sealed conditions to prevent evaporative loss, and glass materials must be used in place of plastics to prevent loss by absorption. In the current study, the antimycobacterial assays performed by a macrodilution method in glass tubes corrected these problems and consequently reproducible results were obtained. In addition, the screening method permitted the detection of resistance by M. tuberculosis to INH, RMP and even for EMB (10,29).