Abstract The aim of the present study was to identify whether monocytic TNFα secretion patterns could serve as a potential phenotypic discriminator for periodontal disease susceptibility within insulin-dependent diabetes mellitus (IDDM) patients. In 32 IDDM individuals the lipopolysaccharide (LPS) stimulated monocytic TNFα secretion dose-response characteristics were analyzed and related to two different periodontal status categories. Diabetics were divided into group A (gingivitis or mild periodontal disease) and group B (moderate to severe periodontal disease). In addition, 17 non-diabetic individuals with various degrees of periodontal disease served as control patients. Diabetics as a group had a significantly higher monocytic TNFα production in response to increasing Porphyromonas gingivalis A 7436 lipopolysaccharide concentrations (0, 0.003, 0.03, 0.3 and 3.0 μg/ml) as compared to non-diabetic patients with gingivitis or adult periodontitis (p <0.05). A significant difference in the dose response was also noted in the level of TNFα secreted as a function of P. gingivalis LPS concentrations between group A and B diabetics, as determined by two-way repeated measurements ANOVA (p <0.05). Furthermore, there was no significant difference in the mean HbA1C between the two diabetic groups, and the TNFα level was not significantly associated with the HbA1C level within diabetic patients. These data suggest that the diabetic state results in an upregulated monocytic TNFα secretion phenotype (4.6-fold increase) which, in the presence of Gram-negative bacterial challenge, is associated with a more severe periodontal disease expression. In addition, approximately 40% (10 of 24) IDDM periodontitis patients in group B demonstrated a 62-fold elevation in TNFα secretion relative to non-diabetic gingivitis or periodontitis patients and a 13.5-fold increase relative to IDDM group A (gingivitis or mild periodontitis) patients.