Rasagiline is a second-generation potent, irreversible and selective inhibitor of monoamine-oxidase type B (MAO-B), which has been evaluated for the treatment of Parkinson's disease. Rasagiline also possesses neuroprotective properties that are independent of its MAO inhibitory activity. Unlike selegiline, rasagiline has no amphetamine-like metabolites and its major metabolite, 1-(R)-aminoindan, has demonstrated favourable pharmacological activity in experimental studies. Rasagiline has shown significant beneficial effects as monotherapy in the treatment of early Parkinson's disease. Monotherapy with rasagiline 1 or 2 mg once daily significantly attenuated the worsening of symptoms, compared with placebo, in patients with early Parkinson's disease in a randomised, double-blind trial (n = 404). Furthermore, patients treated with rasagiline for 12 months had less functional decline than patients whose treatment was delayed for 6 months (n = 371). In patients with moderate-to-advanced disease receiving background therapy with levodopa and additional anti-parkinsonian medications (n = 1159), rasagiline 0.5 or 1 mg once daily reduced the daily 'off' time by 0.49-0.94 hours relative to that in placebo recipients in two randomised, double-blind trials. The efficacy of rasagiline 1 mg once daily was similar to entacapone 200 mg administered with each levodopa dose. Rasagiline was generally well tolerated in clinical trials as both monotherapy and when administered with other antiparkinsonian drugs. Adverse events with rasagiline were generally similar in frequency to those seen in placebo or entacapone recipients.