Twelve patients with refractory rheumatoid arthritis were treated with weekly pulse methotrexate in a double-blind, placebo-controlled, crossover study. After 13 weeks of therapy, patients receiving methotrexate showed greater improvement, judged by degree of joint swelling and tenderness, duration of morning stiffness, and subjective assessments of clinical condition, compared to those receiving placebo (p less than or equal to 0.002). This improvement was associated with a decrease in sedimentation rate and decreases in levels of IgG, IgM, and IgA; no changes were seen in serum rheumatoid factor titer or complement protein levels. Proportions of mononuclear cell subsets that were abnormal before treatment (decreased percentage of total T cells, increased percentage of monocytes) improved toward normal after therapy with methotrexate. However, no changes were seen in elevated pretreatment Leu-3/Leu-2 ratios, in in-vitro proliferative responses of lymphocytes to mitogens, or in immunoglobulin secretory responses to pokeweed mitogen. Weekly pulse methotrexate is effective in the short-term treatment of refractory rheumatoid arthritis. Little evidence for cellular immune suppression was associated with this clinical benefit.