The B-lymphocyte is the tuner of humoral immunity. Following recognition of the antigen, and with significant collaboration with T-cells, B-cells become activated and secrete immunoglobulins. The lung hosts a small number of B-lymphocytes, but their role in various lung diseases is not yet fully understood. In chronic obstructive pulmonary disease (COPD ) and bronchial asthma, there appears to be activation of B-cells, at least at the level of the bronchial mucosa. This may indicate an increased alarm mechanism in the immune system, possibly due to microbial colonization of the bronchial tree, or support the theory of development of an autoimmune mechanism in COPD . Pneumon 2008; 21(1):196–199