Several selective and reversible monoamine oxidase inhibitors (MAOIs) have recently become available. Preliminary studies suggest that these compounds have antidepressant effects and may offer significant safety and side effect advantages over classical MAOIs. Pilot studies with 1-deprenyl, a selective MAO-B inhibitor, indicate that it may be most effective for patients with nonendogenous depression and for those (endogenous or nonendogenous) who present with certain reverse vegetative signs. The drug appears ineffective in depressed patients with associated panic attacks and phobic symptoms. An alternative approach in the development of safer, effective MAOIs is the use of rapidly reversible MAO-A inhibitors, such as moclobemide, that carry less risk of a hypertensive reaction and yet appear to be effective antidepressants. As selective MAO-A and MAO-B inhibition may be effective in different depressive subtypes and may have different side effects, these drugs are valuable pharmacologic probes for studying the biochemical bases of depressive disorders.