This is a prospective, multicentre phase II study in adult patients with documented MMM and requiring therapy for their disease. Patients will be treated every 3 weeks with 4 mg zoledronic acid (Zometa), administered by a 15 min. intravenous infusion. Study duration is 36 weeks (12 infusions). After the study it is recommended to continue treatment until disease progression, or the occurrence of unacceptable treatment-related toxicity.