Thalidomide, the prototype of a new class of agents active against multiple myeloma (MM), exerts synergistic/additive effects when combined with other drugs. The aim of this study was to compare the toxicity and efficacy of thalidomide alone and in combination with oral melphalan. Patients with advanced MM received 100 mg/day oral thalidomide escalated weekly up to 600 mg/day (n=23; T group), alone or with 0.20 oral mg/kg/die melphalan administered monthly for four consecutive days (n=27; TM group). A>/=50% paraprotein reduction was observed in 59% of TM compared with 26% of T patients (P=0.009); three TM patients were found to have an absence of paraprotein by immunofixation. After a median follow-up of 13 months (range 6-32), progression-free survival (PFS) at 2 years was significantly longer in the TM group (61 versus 45%; P=0.0376), whereas overall survival did not differ significantly. Toxicity was not significantly greater with the combination therapy; although DVT was more frequent (11 versus 4%), as was grade 3 leukopenia (30 versus 13%; P=0.073), there were no cases of severe infection. Thalidomide administered with oral melphalan improved response rates and PFS in patients with advanced MM without significantly increasing severe toxicity.