The acidic soluble fraction of whole saliva of type 1 diabetic children was analyzed by reversed phase (RP) 1 -HPLC-ESI-MS and compared with that of sex-and age-matched control subjects. Salivary acidic proline-rich phosphoproteins (aPRP), histatins, ␣-defensins, salivary cystatins, statherin, proline-rich peptide P-B (P-B), betathymosins, S100A8 and S100A9*(S100A9* corresponds to S100A9 vairant lacking the first four amino acids), as well some naturally occurring peptides derived from salivary acidic proline-rich phosphoproteins, histatins, statherin, and P-B peptide, were detected and quantified on the basis of the extracted ion current peak area. The level of phosphorylation of salivary acidic proline-rich phosphoproteins, histatin-1 (Hst-1), statherin and S100A9* and the percentage of truncated forms of salivary acidic proline-rich phosphoproteins was also determined in the two groups. The study revealed that statherin, proline-rich peptide P-B, P-C peptide, and histatins, were significantly less concentrated in saliva of diabetic subjects than in controls, while concentration of ␣-defensins 1, 2 and 4 and S100A9* was higher. The low concentration of P-C peptide was paralleled by high levels of some of its fragments. On the whole, the study highlighted the severe impairment of the repertoire of peptides involved in the safeguard of the oral cavity in children who have diabetes, as well as an higher concentration of the proinflammatory mediator S100A9* with respect to healthy children. Molecular & Cellular Proteomics 9:2099 -2108, 2010.Type 1 diabetes mellitus is a disease with universal distribution, affecting all populations (1) with an incidence increasing in Europe (2). Because type 1 diabetes involves many organs and tissues, signs and symptoms of diabetes can occur in the oral cavity. Indeed, several studies have shown that the prevalence, severity, and progression of periodontal diseases are significantly increased in diabetics, and the pathology is considered an important risk factor for periodontitis (3). The study of Lalla et al. (4) showed an association between diabetes and the increased risk for periodontal destruction even very early in life. Flow rate and composition of saliva are crucial for the maintenance of oral cavity health, and both have been found altered in diabetic subjects, although with contradictory findings. For instance, several studies reported a reduced resting salivary flow rate in adults and children who have type 1 diabetes with respect to healthy subjects (5-10), but it was also observed that stimulated saliva of diabetics and controls did not significantly differ (11,12). Total protein concentration of saliva was found either increased or not affected by the diabetic status. Lopez et al. (9) reported higher urea and total protein salivary content in diabetic children than in controls. Conversely, a study on 35 adult insulin-dependent diabetics demonstrated that they did not show a decreased saliva concentration of several innate antimicrobial factors (lysozyme, lactoferri...