ABSTRACTThe literature on in vitro tests of sensitivity to brain antigen in multiple sclerosis is summarized in the tables. A study is presented using leukocyte migration in agarose as test system and a wide range of concentration of bovine encephalitogenic protein as antigen. Definite reactivity was seen in 12 out of 28 patients with MS. Some occurred in patients who had had no signs of disease activity for at least 5 years. Reactivity occurred more often in patients with active disease studied within 5 days after a relapse. The significance of the in vitro reactivity is briefly discussed.