Purpose: To compare phagocytic activity of peripheral blood neutrophils from subjects with and without periodontal disease and evaluate the effects of periodontal therapy in individuals with similar levels of resolution of inflammation at the end of treatment. Materials and Methods: To compare the phagocytic activity of neutrophils, peripheral blood was collected from 27 control subjects with a healthy periodontium and 28 periodontitis subjects before and after treatment. The phagocytosis of killed Saccharomyces cerevisiae, pre-sensitised or non-sensitised with fresh serum from the donor, was quantified and a phagocytic index was calculated as the mean number of yeast cells phagocytised by the percentage of neutrophils involved in phagocytosis. Results: Prior to periodontal treatment, subjects with periodontitis exhibited significantly lower neutrophil phagocytic activity than control subjects with a healthy periodontium. Periodontal treatment significantly improved in clinical periodontal status and resulted in significantly increased phagocytosis of both pre-sensitised (from 113.0 pre- to 157.0 post-treatment, P = 0.02) and non-sensitised S. cerevisiae (from 1.5 pre- to 3.5 post-treatment, P = 0.001), to levels observed in control subjects. Conclusions: The phagocytic activity of peripheral blood neutrophils from subjects with periodontal disease was lower than that of healthy controls. Subjects who underwent non-surgical periodontal treatment and strict supportive therapy for 6 months showed improved phagocytic activity in peripheral blood neutrophils. The phagocytic index values from subjects with periodontal disease after treatment achieved those found in the control group. Keywords: neutrophils, periodontal therapy, periodontitis, phagocytosis