Abstract: PT was performed by 2 methodes: 1- Needle prick. 2-- Intra dermal injection of normal salin. 83 % of BD patients presented a positive PT. Control subjects were composed of 101 healthy person, 46 Rheumatoid Arthritis, 5 Ankylosing Spondylitis, 18 Systemic Lupus Erythematosus (SLE). 3 Sclerodermia, and 1 permatomyositis. Among them 16% presented a positive PT. Only 3% had a positive PT with both needle prick and normal salin method. 9% had a positive test with needle prick alone and 4% with normal salin alone. All positive results in the control group were of papule type (1+ positive). The pustular type reaction was never observed in other subjects apart BD patients. We conclude that a pustule type response (2+ or 3+ positive PT) is highly suggestive of BD and may suffice for the diagnosis, if present with one of the major symptoms of the disease (as proposed in the diagnosis criteria of Diisen). A papule type reaction, if present with both needle prick and normal salin, may have the same value, as it was detected in only 3% of control subjects, If SLE patients are excluded, this percentage falls to 1.2%.