Salivary agglutinin plays a vital biological role modulating the protective effect in the oral cavity by interacting with a broad range of oral pathogens. Here, we describe the first characterization of the O-linked oligosaccharides of salivary agglutinin identified by negative ion liquid chromatography-mass spectrometry. The dominating structures were neutral or monosialylated core 1 (Galbeta1-3GalNAcalpha1-Ser/Thr) and core 2 (Galbeta1-3(GlcNAcbeta1-6)GalNAcalpha1-Ser/Thr) structures extended by fucosylated oligo-N-acetyllactosamine units. Oligosaccharides detected as [M-H](-) or [M-2H](2)(-) ions ranged from the disaccharide Galbeta1-3GalNAcol up to structures of almost 4000 Da, corresponding to core 1/2 structures with five N-acetyllactosamine units and 11 fucoses. Fucose was found either as terminal or internal blood group H structures in type 1 (Galbeta1-3GlcNAcbeta1-R), type 2 (Galbeta1-4GlcNAcbeta1-R) and type 3 (Galbeta1-3GalNAcalpha1-Ser/Thr) units, where the chains also could be fucosylated on GlcNAc yielding repeated Lewis a/b or Lewis x/y structures. Sialylation was located either at the non-reducing end of the N-acetyllactosamine chains as sialyl-Lewis x or as sialyl-T (NeuAcalpha2-3Galbeta1-3GalNAcalpha1-Ser/Thr) type structures with or without further extension of the C-6 branch of GalNAc with neutral fucosylated N-acetyllactosamine chains. The data indicated that sialylation, fucosylation and type 1 N-acetyllactosamine termination are important regulatory elements for controlling the oligosaccharide chain length. Furthermore, it was shown that these regulatory oligosaccharide elements could be utilized by the pathogen Helicobacter pylori to colonize the oral cavity, reside in dental plaque and serve as a reservoir for reinfection after successful clearance of H. pylori gastric infection.