Horse gram (Dolichos biflorus) is widely consumed in the tropical south Asian countries including rural areas of India. Since D. biflorus agglutinin (DBA) is an important dietary lectin in horse gram, we have studied its effect on the degranulation of mast cells and basophils of atopic subjects. Allergy to horse gram lectin has not been reported so far. Skin prick test (SPT) was performed with 100 microg/mL of DBA. DBA-specific IgE was detected by dot-blot, and ELISA. Histamine release (HR) assay was carried out using leukocytes from non-atopic and atopic subjects, and rat peritoneal exudate cells. Among the atopic group, 10 of 48 subjects (21%) were found to be positive for DBA by SPT, and none were positive in the non-atopic group (n=20). Two subjects out of the ten who tested positive for DBA by SPT were found to be sensitized to DBA as revealed by the presence of specific IgE by ELISA and dot-blot. The HR was found to be 2- to 3-fold higher in DBA-allergic subjects than in non-atopic and atopic subjects. Basophil HR by DBA was found to be similar in both non-atopic and atopic subjects. However, DBA induces activation of mast cells in vivo in a sub-population (21%) of atopic subjects. Two subjects have been identified as having food allergy to horse gram based on the presence of DBA-specific IgE with a positive correlation to basophil HR. This is the first report of food allergy to horse gram, and DBA has been identified as an allergen.