Dendritic cells (DCs) and their precursors play important roles, not only as antigen presenting cells, but components of the immunoregulatory network. Depending on their lineage, activation and differentiation state, DCs can promote a strong T-cell response or a state of anergy, and can polarize the T helper response in the direction of TH1 or TH2. The lung comprises one of the major interfaces between the host and the environment and regularly comes into contact with antigens, allergens and pathogens. Inflammation in response to these stimuli must be very carefully regulated in the lung since perturbations, especially of a chronic nature, can result in immunopathology that interferes with the lungs' critical function of gas exchange. Especially in disease states such as chronic obstructive pulmonary disease, which has been associated with a chronic TH1 response, and asthma, which is TH2-driven, the ability to access and characterize DCs and their precursors is critical to the understanding of immune modulation in these processes. In this report we will demonstrate that mature DCs and their monocytoid and plasmacytoid precursors can be sampled in the lung by the minimal invasive procedure of broncho-alveolar lavage (BAL) despite their relative scarcity and can be detected by rare event multiparameter flow cytometry.