An unusually high prevalence (45%) of serum antibodies to human T cell leukemia virus type I (or to an antigenically related virus) in comparison with that observed against other viral pathogens (human immunodeficiency virus type 1, herpes simplex virus, human cytomegalovirus, varicella zoster virus, and respiratory syncytial virus) has been observed in a group of Bismam Asmat (Papua) subjects, living in a very limited and geographically isolated area of Indonesian New Guinea.