Religious Beliefs. Although the Nasioi also believed in supernatural beings who inhabited the forests and rivers, the outstanding characteristic of traditional Nasioi religion was the belief that humans are dependent on the spirits of the dead ( ma'naari ) for material well-being. Offerings of special food (e.g., pork) and invocations were made to ensure the favorable attention of these spirits. When Roman Catholic missionaries began to work among the Nasioi, many converts seemed to regard the Christian pantheon as a set of especially powerful ma'naari. Seventh-Day Adventist missionaries arrived in Nasioi territory in the 1920s and Methodists in the 1930s. After the disruption of World War II and with growing discontent over their colonial situation, the Nasioi began to display cargo-cult beliefs. These often syncretized traditional beliefs and introduced Christian notions, with the goal of changing Nasioi life to be more like that of the European colonizers. The Tok Pisin term longlong lotu or "crazy church" was sometimes applied to these beliefs and practices, which were attacked by the colonial administration. At present, adherence to Christianity seems to have suffered while various cargo cults thrive.
Religious Practitioners. Nasioi did not have full-time religious practitioners. Individuals were thought to have special knowledge (e.g., of sorcery), usually derived from a familiar spirit. After missionization, a number of Nasioi became teachers and catechists, and the present Roman Catholic bishop of Bougainville is a Nasioi. At least one Nasioi has sustained his position as a cargo-cult leader for more than two decades.
Ceremonies. Propitiation of ma'naari and life-cycle events occasioned the most common ceremonies; the former kind were usually individual activities. Missionization meant Christian observances, which may have fallen off during recent unrest. Cargo-cult ceremonials often relate to the remains of the dead, showing continuity with the past.
Arts. Although utilitarian objects like combs were occasionally decorated, the Nasioi seem to have emphasized music and dance over graphic and plastic arts. Slit gongs, wooden trumpets, panpipes, and the Jew's harp were employed, and dances sometimes involved cross-gender performances. Modern Nasioi enjoy "string bands" and other Pacific adaptations of Western music.
Medicine. Illness was thought to be most often the result of sorcery. Various plant materials were employed in curing, but the ultimate efficacy of cures depended upon the assistance of spirit helpers. Some individuals were thought to be especially skillful at dealing with bone and muscle injury. Western medicine is today valued for certain ailments; despite the initial success of a malaria eradication campaign, the disease has once again become a serious health problem.
Death and Afterlife. Nasioi believed most deaths, except those of the very young and very old, were ultimately caused by sorcery or malevolent spirits. A human was thought to have two souls; the one that stayed near the living was important, as noted. Informants were vague about the fate of the other soul or shadow. Nasioi cremated the dead, though they sometimes preserved the lower mandible in a clanmember's house. These rites were traditionally important, but following contact missionaries introduced burials and cemeteries. Since the 1970s, however, cremation has revived, as Christian practice has weakened and cargo cults have maintained vitality.