During the study's sixth year we will continue follow-up of the cohorts of persons who had multiple sclerosis (MS) on April 1, 1970 in King-Pierce Counties, Washington, and Los Angeles County, California. The fifth-year follow-up will be analyzed. Additional patients with a progressive course will be enrolled in the longitudinal study; exacerbating patients will be enrolled to replace any vacancies which occur in that group. Determinination of possible relationships between immune responses to certain viral and brain antigens and tissue types and clinical course will continue. The verification of diagnoses and collection of historical data, tissue types, and serologic data on the participants in the study of families with more than one case of MS will continue. The case-control study of younger, recently diagnosed cases of MS, with childhood friends as controls, will enter the data collection stage, using mothers of cases and controls as additional informants. Termination of the study of the apparent time-space cluster in 1954-55 in King County will be considered this next year, since early analysis suggests this cluster may not be real. Further analysis will be carried out on the relationship between age at migration and risk of MS.