A (massive) multicenter study of 3,000 patients has demonstrated that skin tests to penicillin G and penicilloyl-polylysine (PPL-now commercially available) predict and confirm penicillin allergy. Of patients with a history of penicillin reaction, 19% were positive to either, compared to 7% of controls. A history of anaphylaxis led to 46% positive. Of those with a history of urticaria 17% were positive, and those with maculopapular eruptions did not differ from controls (7% positive). Challenge with penicillin led to a reaction in 6% with a positive history (compared to 2% with a negative) and 67% with a combined positive history and positive skin test (to either).