Total lymphoid irradiation (TLI) has been reported to delay deterioration in patients with progressive multiple sclerosis and other autoimmune disorders. METHODS--In an open trial, the effect of TLI combined with a one year course of low dose prednisone was compared to the effect of sham TLI and TLI only in a prior double-blind study of patients with progressive multiple sclerosis. RESULTS--Twenty-seven patients receiving TLI combined with corticosteroids had significantly greater lymphocytopenia in the year post-therapy than those receiving TLI only or sham TLI and Kaplan Meier product-limit survival analysis showed significantly less progression in the TLI plus steroid group over 4 years of follow-up. No difference in lymphocytopenia or progression was found with TLI plus corticosteroid therapy when the spleen was removed from the field of irradiation. CONCLUSION--These results lend further support to the hypothesis that TLI may be effective in progressive MS, and indicates that adding low-dose prednisone may enhance this effect. The study also suggests that TLI may be equally effective whether or not the spleen is irradiated.