This thesis examines C. neoformans and the meningitis it causes, based largely in Papua New Guinea (PNG). Investigation of possible environmental associations in PNG revealed that few E. camaldulensis survive experimental planting, while E. tereticornis is endemic. In Port Moresby E. confertiflora, E. papuana and E. alba are common. Examination of 1130 specimens from plant, bird and animal sources, failed to identify the ecological niche of C. neoformans in PNG. Epidemiological study of 96 patients presenting to Port Moresby General Hospital with cryptococcal meningitis from 1972-1993 showed an annual incidence of 33 cases per million population of Central Province and the National Capital District. 21 of these were infected with var. gattii and 12 with var. neoformans. On average 11 cases of cryptococcal meningitis present here annually. In this study geographical clustering, male predominance and possible seasonal variation were found. Eleven patients with cryptococcal meningitis were prospectively diagnosed and isolates biotyped. Seven isolates were var. gattii (one patient with diabetes mellitus) and four were var. neoformans. The latter came from adult patient with HVI infection, tuberculosis or Plasmodium vivax malaria. Five patients (45.5%) died; the 2 var. neoformans HIVI infected men and 3 adult var. gattii patients. In PNG, where var. gattii has been predominant in the immunocompetent, var. neoformans is emerging amongst immunosuppressed patients, notably those with HIVI infection. These studies confirm the high prevalence in PNG of meningitis caused by C. neoformans var. gattii in immunocompetent individuals. Potential mammal and plant sources are similar to those found in Australia.