Preliminary clinical results indicate that the cytostatic agent mitoxantrone is an effective and very tolerable substance for treating multiple sclerosis (ms). Our own experience, added to the findings of other pilot studies, seems to indicate that disease progression can be slowed in a majority of patients with rapidly progressive ms. Mitoxantrone is mainly excreted by the hepato-biliary pathways and therefore it can be used in patients with renal insufficiency or chronic cystopyelitis, a frequently occurring condition in ms. The side effects observed in our therapeutic scheme which could be attributed to mitoxantrone were tolerable. Mild gastrointestinal complaints were occasionally reported and vomiting was very rare. A carcinogenic effect from mitoxantrone has not been reported. A decrease in the leucocyte count is to be expected 6-15 days following treatment administration. Potential cardiotoxicity represents the primary long term adverse reaction and thus patients with cardiovascular risk factors should not be treated with mitoxantrone. Once a cumulative dosage of 140 mg/m2 is reached cardiac function tests, including echocardiography with measurement of the left ventricular ejection fraction, should be routinely carried out preceding each treatment administration in all patients. Mitoxantrone is currently not licensed for use in patients with ms and therefore should be restricted to patients with rapid disease progression where other generally accepted treatment modalities have failed.