The extensive laboratory investigations included hemoglobin level, hematocrit; erythrocyte sedimentation rate; white blood cell count; differential blood cell count; total eosinophil count; liver and kidney function tests; determination of levels of glucose, protein, complements, circulating immune complexes, and cryoglobulin; serologic tests for rheumatoid factor, IgE and antinuclear antibodies, hepatitis B, syphilis, antistreptolysin titer, Strongyloides, and anti–double-stranded DNA; and radioallergosorbent tests (RASTs) for inhalation allergens (mixtures of rodents, birds, fungi, grass pollen, birch pollen, mugwort pollen, cat dander, dog dander, and house dust mites), food allergens (mixtures of crustaceans, fish, meat, wheat, fruits, vegetables, soy, peanuts, and peas), and other allergens if suspected. Urinalysis and examination of stools for parasites and occult blood were performed. Smears from the throat were cultured for streptococci, and smears from the vagina were investigated for Candida organisms. Radiographs of the chest, paranasal sinuses, and teeth were obtained to search for possible infections or malignancies. Skin biopsy specimens were obtained from urticarial lesions. Each patient was given a routine physical examination and provocation tests for physical urticarias as described by Henz et al31 (dermatographism and cold urticaria). Other physical provocation tests were performed when deemed necessary. If the patient used drugs, a determination was made as to whether there was a possible time relationship with the urticaria, and treatment with all drugs was discontinued or replaced with chemically unrelated equivalents. Suspected underlying diseases were treated whenever possible to find out whether there was an association with chronic urticaria. An elimination diet (ie, a diet without salicylates, dyes, benzoates, sorbic acid, sodium glutamate, sulfites, antioxidants, sodium nitrate, parabens, vasoactive amines, histamine liberators, sugar, yeast, spices, coffee, crustaceans, fish, meat, eggs, milk products, and potatoes) was prescribed for at least 3 weeks to screen for adverse reactions to food. Drug provocation tests and oral food rechallenge tests were performed when necessary.