Human T-lymphotropic virus type I (HTLV-I), the etiological agent of adult 
T-cell leukemia/lymphoma, also appears to be the cause of tropical spastic 
paraparesis, a chronic myelopathy reported in several different regions of the 
world. The prevalence of antibodies to HTLV-I in patients with chronic 
neurodegenerative disorders other than tropical spastic paraparesis and in 
patients with some muscle inflammatory disorders has been investigated. IgG 
antibodies to HTLV-I were measured in the sera and/or cerebrospinal fluid from 
82 Guamanian patients with amyotrophic lateral sclerosis and 
parkinsonism-dementia, 164 Guamanian normal controls, 10 patients with kuru from 
the Eastern Highlands of Papua New Guinea, 4 patients with Viliuisk 
encephalomyelitis from the Iakut region of eastern Siberia, 45 Italian patients 
with multiple sclerosis, and 56 patients with polymyositis (49 from the United 
States and 7 from Jamaica). As determined by enzyme-linked immunosorbent assay, 
Western immunoblot, and gelatin particle agglutination techniques, serological 
evidence of HTLV-I infection was found in 1 patient with amyotrophic lateral 
sclerosis and 1 control subject from Guam, and in 1 patient from the United 
States and all 7 Jamaican patients with polymyositis. Except for the high 
seropositivity rate among the group of Jamaican patients with polymyositis, our 
data indicate that HTLV-I is an unlikely causative agent in the spectrum of the 
neurological diseases examined. The seropositivity of the 7 Jamaican patients 
with polymyositis requires further study.