Introduction: the demand for drug discovery today; the impact of atmospheric pressure ionisation. Part 1 Instrumentation: a mass spectrometry primer. Part 2 Experimental strategies: ion chemistry and fragmentation; the LC/MS experiment; sample preparation and handling for LC/MS in drug discovery. Part 3 Applications: mass spectrometry in combinatorial chemistry; drug hydrophobicity and transport; the mass spectrometer in drug metabolism; mass spectrometry-assisted applications of stable-labeled compounds in pharmacokinetic and drug metabolism studies; cassette dosing in drug discovery; applications of microdialysis/mass spectrometry to drug discovery; future directions for mass spectrometry in drug discovery.