A chronic and extensive distinctive pruritic vesiculobullous eruption in a young woman resembled dermatitis herpetiformis clinically and erythema multiforme histologically. The most remarkable feature was the regular premenstrual exacerbation. Study revealed that flares could be excited by progesterone and progestational compounds. Within seven hours a single dose of progesterone induced pruritus, and a clinical flare associated with marked degranulation and later disappearance of the circulating basophil leukocytes. In turn, clinical remission could be induced by estinyl estradiol for oral administration in a dosage sufficient to suppress ovulation. Oophorectomy was followed by complete involution of all clinical signs and symptoms. The eruption is viewed as an autoimmune phenomenon triggered premenstrually by endogenous progesterone.