An undergraduate LC-MS experiment is described for the identification and quantitative determination of acetaminophen, acetylsalicylic acid, and caffeine in commercial analgesic tablets. This inquiry-based experimental procedure requires minimal sample preparation and provides good analytical results. Students are provided sufficient background information to allow them to independently develop chromatographic separation and analytical-analysis procedures using a liquid chromatograph-mass spectrometer. The experiment can be conducted in two consecutive, 3-h laboratory periods. Students gain experience using state-of-the-art analytical instrumentation that simultaneously provides chromatographic, ultraviolet, and mass spectrometry data. The efficiency of concurrently collecting three different types of experimental data translates into more time for inquiry-based investigation, instructional emphasis on theory, and data manipulation. (Contains 3 notes and 1 figure.)