The results obtained in this study indicate that there are various patterns of hypersensitivity to penicillin. In order to detect these variations it is suggested that two antigens, penicillin and penicilloyl-polylysine, be employed to test for both serum and skin sensitivity. Absolutely accurate predictions cannot be made from these tests, but it is felt that their use will minimize untoward reactions of the anaphylactic type in patients thus screened for penicillin allergy.