The proposed research is intended to determine if supplementation of relatively high dose vitamin D in chronic urticaria patients receiving omalizumab will result in continued symptomatic control of hives after the discontinuation of omalizumab.

Inclusion Criteria:

• Physician diagnosed chronic urticaria
• Currently be receiving omalizumab therapy for the treatment of chronic idiopathic urticaria and be well controlled with a USS <25

Exclusion Criteria:

• Not capable of informed consent.
• Not capable of answering the questionnaire.
• Subjects with a pure physical urticaria.
• Pregnant or lactating women.
• Subjects with hypercalcemia (calcium > 10.3 mg/dl) or renal insufficiency (GFR <50 ml/min).
• Subjects with prior anaphylaxis to omalizumab.
• Currently taking high dose vitamin D supplementation.
• Prior high dose vitamin D supplementation for urticaria with failure.
• Baseline 25(OH)D >80 ng/ml
• Subjects with sarcoidosis, hyperparathyroidism, histoplasmosis, lymphoma or tuberculosis