Vibratory angioedema is a rare form of physical angioedema. A Mexican-American boy presented with vibration-related prolonged angioedema of the hands at age 16. After the use of a controlled vibratory stimulus, 10 volunteers and seven members of the family (three generations) developed expected transient erythema and whealing reaction of the skin at the site of contact. However, with the same vibrating stimulus the patient developed large erythematous swelling that lasted for 12 hr. Vibratory challenge study revealed a rapid rise and fall in plasma histamine. No increase in levels of plasma histamine were detected from the nonstimulated arm. Prausnitz-Küstner testing was negative. Light and electron microscopic study of the mast cell revealed degranulation and extensive fragmentation of the granules from the stimulated site. No degranulation was seen in the contralateral unstimulated site. A state of tolerance to vibration was induced by graded increased exposure to vibratory stimulus and the patient's clinical problem was eliminated.