A serological investigation, covering many localities throughout Western New Guinea (Irian Jaya) in 1958-1961 showed that: A general endemicity of arbovirus infections rather than sporadic epidemics, exists in the southern lowlands--large differences exist in geographical distribution of these viruses especially when comparing coastal areas of the southern, with those of the northern and north western parts of the island--in both arbovirus groups noticeable differences in altitude were observed corresponding with the epidemiology of malaria in Irian Jaya--in one locality there was a specific virus prevalence, notably Sindbis virus, within a group--historical and serological evidence suggests that antibody detected to Dengue 2 virus, merely in adult humans, in the coastal area was due to exposure before migration from Indonesia to New Guinea--comparable results were archieved with similar surveys by other workers in Papuan New Guinea and Northern Queensland.