We present a case of anaphylactic shock induced by exercise following celery ingestion. The possible mechanism of food-dependent exercise-induced anaphylaxis (FDEIA) and the laboratory tests for its diagnosis are discussed. We evaluated spontaneous, celery-allergen-induced, and anti-FcepsilonRI-antibody-induced histamine release from basophils obtained from the patient, 2 celery-allergic controls, and 3 healthy controls. Buffers of increasing osmolarity were used to mimic conditions of vigorous physical exercise. Only the patient's basophils showed an increase in spontaneous, anti-FcepsilonRI antibody-induced and allergen-induced histamine release under physiological conditions and with slightly increased medium osmolarity. To our knowledge, this is the first report on the possible role of increased histamine releasability in the pathogenic mechanism of FDEIA. We suggest that FDEIA results from increased histamine releasability triggered by physical effort after exposure to a sensitizing food allergen.