Monoamine oxidase (mao) inhibitors are antidepressants with potentially severe side-effects. For this reason, the registration of this drug was suspended for some time when safer alternatives became available. However, mao inhibitors can be very effective in cases where depression has proved to be treatment resistant. Consequently, last year tranylcypromine was re-registered for use in the Netherlands. Since mao inhibitors have been used only sporadically in the Netherlands over the last few years, health professionals have only limited knowledge about the side-effects. On the basis of a recent case, we discuss the two most important side-effects of using mao inhibitors, namely hypertension and orthostatic hypotension. We discuss the possible causes and suggest ways on which these two side-effects can be prevented, or treated, should they arise.