Beta-lactam allergy is the most prevalent drug allergy. Drug eruption is the most common symptom whereas life-threatening anaphylaxis is rather rare. A recently published study (Journal of Allergy and Clinical Immunology, January 2011, Vol. 127, p. 218-222) described the safety of a 2-day oral beta-lactam challenge in penicillin-allergic patients, disregarding their penicillin skin test results. In the proposed study the investigators will similarly challenge beta-lactam allergic patients, both children and adults for an extended (5 days) period of time. The study will include patients with a history of a skin rash following beta-lactam administration as well as patients who cannot provide any data on their presumed allergic reaction, disregarding their penicillin skin test results.