Twenty-one patients with multiple myeloma, all relapsed after frontline autologous stem cell transplantation and all relapsed again after or resistant to thalidomide (employed as second line treatment) received bortezomib (1.3 mg/m(2) body surface twice weekly for 2 weeks followed by an interval of 10-12 days) without adjunct of steroids as third line therapy. Three patients died of progressive disease during the first 2 cycles with bortezomib. Eighteen patients received at least 2 cycles and were evaluated for response. According to EBMT criteria, two complete (negative immunofixation) and seven partial (reduction of M-component > 50-75%) remissions were achieved (ITT response rate 42.8%). Duration of response lasted from 2 to 14+ months. Grades 3-4 toxicities (thrombocytopenia, leucopenia, peripheral neuropathy and vasculitis) were observed in seven patients, but no patient interrupted the treatment due to side effects. We conclude that bortezomib alone may induce high quality responses as third line salvage therapy with acceptable toxicity in a significant proportion of homogeneously pre-treated myeloma patients with progressive disease after autologous transplantation and thalidomide.