Human respiratory mucins consist of a family of glycoproteins with different peptides in which glycosylation, the major post-translational phenomenon, is responsible for about 70 to 80% of the weight of these molecules. This glycosylation generates a remarkable diversity of O-glycosidically linked carbohydrate chains, which are expressed as several hundreds of different chains in a single person. These chains, which can vary from one to about 20 sugars, may be neutral, sialylated, or sulfated. They bear multiple epitopes. Some antigenic determinants such as ABO, Leb antigens in secretor individuals, Lea, or X or Y antigens have been identified. There is increasing evidence that, among other functions, this diversity of chains allows many interactions with microorganisms and may be an important factor in maintaining the sterility of the respiratory tree. In certain pathologic situations such as cystic fibrosis, which is associated with colonization by Pseudomonas aeruginosa, the hypothesis of an alteration of this interaction is open.