A longitudinal assessment of clinical, virological and immunological progression in HAM/TSP will be accomplished through periodic testing and evaluation. Asymptomatic seropositive individuals, those with seroindeterminate HTLV-I serology and normal volunteers may serve as controls. Longitudinal standardized neurological examinations will be performed. Longitudinal samples of serum, plasma, and lymphocytes may be obtained from participants. Lumbar punctures may be performed on all participants. These samples will be used for virological and immunological assays. A focus is on the relationships between the characteristics of viral infection, the immune response, and the genetic makeup.