Bacterial antibiotic resistance remains a problem of clinical importance. Current microbiological methods for determining antibiotic resistance are based on culturing bacteria, and may require up to 48 hours to complete. Molecular methods are increasingly being developed to speed the identification of antibiotic resistance and to determine its mechanism. This paper describes a fast and robust method of determining whether and how a particular strain of "E.coli" is resistant to the antibiotic ampicillin, using the Polymerase Chain Reaction. This exercise is designed to help students learn about modern methods for determining antibiotic resistance. (Contains 1 table and 1 figure.)