Specific inhibitors of monoamine oxidase type B (MAO-B) constitute a novel and expanding pharmacological class. At present, only one compound from this class is marketed, selegiline (deprenyl). Other MAO-B inhibitors that are in various stages of development include lazabemide and mofegiline, which are differentiated from selegiline by their greater specificity for MAO-B and the absence of active metabolites. The role of MAO-B in the catabolism of amines (essentially, dopamine and phenylethylamine) and the acceleration of the neurodegenerative process (i.e. oxidative stress) justifies the most common indications for these compounds - Parkinson's disease, Alzheimer's disease, pathological aging and, possibly, depression. The possibility that MAO-B inhibitors may antagonise the evolution of neurodegenerative disorders needs further scrutiny. Selegiline is the most extensively studied MAO-B inhibitor and is marketed for Parkinson's disease in most Western countries. A dosage of 10 mg/day improves motor symptoms and delays the need for levodopa in de novo patients. Adverse effects are rare and trivial, although some reports of changes in blood pressure have to be considered seriously. Long term clinical trials with new MAO-B inhibitors are not available. Current data suggest that these drugs are well tolerated and have a low potential for drug interactions.