Variance in expression of receptors for immunoglobulin G (FcγRs), complement (CR3) and lipopolysaccharide (mCD14) on polymorphonuclear neutrophils (PMNs) and monocytes might affect susceptibility for infection with certain pathogens in periodontitis, a chronic infectious disease of tooth-supportive tissues. Levels of FcγRI, IIa, III, CR3 and mCD14 on PMNs and monocytes were measured in 19 periodontitis patients and 18 healthy controls. Subgingival infection with Aggregatibacter actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) was determined. Activation of PMNs and monocytes in response to stimulation with Aa and Pg was assessed by means of change in mCD14 expression. Periodontitis is associated with an enrichment of the FcγRIII+ monocytes (P = 0·015) with concomitant low mCD14 (P = 0·001). Unadjusted data showed that the subjects culture-positive for Aa (Aa+) had significantly lower expression of monocytic FcγRI (P = 0·005) and FcγRIIa (P = 0·015) than Pg+ subjects. The FcγRI was still lower on monocytes from Aa+ subjects after adjusting for the background factors (P = 0·037). PMNs from Aa+ subjects responded in a hyper-reactive manner, in particular when stimulated with Aa (P = 0·011). Lower FcγRs expression by monocytes is related to a higher susceptibility of a subject to become infected with Aa. The higher proportion of FcγRIII+ monocytes may be involved in the chronicity of this condition. Hyper-reactive PMNs in Aa+ subjects may contribute to accelerated breakdown of tooth-supportive tissues.