Penicillin skin tests are of value in detecting patients at risk of experiencing an immediate or accelerated hypersensitivity reaction. This paper briefly reviews the immunologic aspects of penicillin hypersensitivity, the indications and procedure for using penicillin skin tests, and the interpretation of skin test results. A pharmacy-prepared skin test kit is also described. The penicillin skin test kit can facilitate the proper use of penicillin test reagents.