Non-steroidal anti-inflammatory drugs (NSAIDs) are, as a group, the most frequently consumed drugs worldwide. They also cause the most, and often dangerous, side-effects reported to the US Food and Drug Administration, the majority of which are owing to damage of the gastrointestinal tra ct and kidneys. This explains the continuous interest of pharmacologists, clinical pharmacologists and pharmacoepidemiologists in this group of drugs. Based on an increasing body of data, J. Frolich proposes a simple alternative to the usual chemical classification of NSAIDs, allowing one to predict a drug's major effects according to its relative inhibition of the constitutive and inducible cyclooxygenase isoenzymes.