In most studies of disease modifying antirheumatic drug therapy, in combination with either leflunomide or biological agents, patients are given an additional agent after they have failed treatment with methotrexate (MTX). This review of clinical studies shows that leflunomide is clinically efficacious and well tolerated when added to either sulfasalazine or MTX, as both an initial and ongoing treatment for rheumatoid arthritis (RA). Experience in combining leflunomide with biological agents is limited to a small number of open-label studies with infliximab. According to the opinion obtained at an International Expert Panel Meeting held in Paris in May 2003, leflunomide can be used in combination therapy: 61% of the Expert Panel would use leflunomide with MTX, 71% with sulfasalazine, 43% with infliximab, 33% with adalimumab, 19% with etanercept, and 38% with anakinra. The Expert Panel stated that the combination of leflunomide and infliximab warrants a prospective, randomized, controlled trial in patients with incomplete clinical responses to leflunomide monotherapy, provided leflunomide is started first, without a loading dose, and infliximab is added after good tolerability to leflunomide has been established. The Expert Panel concluded that combination therapy with leflunomide has a place in the treatment of RA. Caution is advised, however, when using combination treatments and, therefore, the patient's safety should be carefully monitored.