Recently, immediate allergic reactions, including anaphylaxis, after Pachycondyla chinensis ant stings have been frequently reported in Korea. To estimate the prevalence of these reactions and the sensitization rate to P chinensis, we undertook a visit-questionnaire survey of the 327 adult residents living in a town in an ant-infested area in Korea. Skin prick tests with 6 common inhalant allergens, 3 bee venom allergens, and P chinensis whole body extract were performed on all ant-allergic subjects, on 86 asymptomatic residents, and on 37 controls outside the area. The serum-specific IgE to P chinensis extract was determined by ELISA. Seven subjects (2.1%) reported that they had experienced systemic allergic reactions to P chinensis stings; 4 of them had anaphylactic reactions. Large local reactions occurred in an additional 5 subjects (1.6%). All subjects with systemic allergic reactions had positive skin prick test results to P chinensis extract, whereas 23.3% of asymptomatic residents and 2.7% of the controls showed positive skin prick test results. The serum-specific IgE level was significantly higher in the subjects with systemic reactions than in the subjects with local reactions, the asymptomatic sensitizers, and the nonatopic controls. Sensitization to bee venom was found in 25% of the P chinensis -allergic subjects; this was significantly higher than the 3% rate seen in nonsensitized subjects. In conclusion, we report a 2.1% prevalence of systemic allergic reactions after P chinensis stings, based on self-reported symptoms, in an ant-infested area in Korea.