This study aimed to define the bacterial microbiota in the lungs of healthy individuals and assess its relationship to upper airway populations. Using molecular methods, including 16S rDNA-Q-PCR and deep sequencing, the researchers sampled respiratory flora at multiple sites in six healthy individuals. The results showed that bacterial communities from the lungs were indistinguishable from those in the upper airways but were 2 to 4 logs lower in biomass. Lung-specific sequences were rare and not shared among individuals, indicating no unique lung microbiome. The study concluded that the respiratory tract harbors a homogenous microbiota that decreases in biomass from the upper to the lower tract, with the healthy lung containing low levels of bacterial sequences largely indistinguishable from upper respiratory flora. These findings provide baseline data for healthy subjects and sampling approaches for sequence-based analysis of diseases.This study aimed to define the bacterial microbiota in the lungs of healthy individuals and assess its relationship to upper airway populations. Using molecular methods, including 16S rDNA-Q-PCR and deep sequencing, the researchers sampled respiratory flora at multiple sites in six healthy individuals. The results showed that bacterial communities from the lungs were indistinguishable from those in the upper airways but were 2 to 4 logs lower in biomass. Lung-specific sequences were rare and not shared among individuals, indicating no unique lung microbiome. The study concluded that the respiratory tract harbors a homogenous microbiota that decreases in biomass from the upper to the lower tract, with the healthy lung containing low levels of bacterial sequences largely indistinguishable from upper respiratory flora. These findings provide baseline data for healthy subjects and sampling approaches for sequence-based analysis of diseases.