The microbiologic history of noma was reviewed. Studies have associated the disease process with large numbers of fusiform bacilli and spirochetal organisms. In order to study the microbiology of the staging and infection periods of noma 62 Nigerian children, aged 3-14 years, 22 children had acute necrotizing ulcerative gingivitis (ANUG) and were also malnourished, 20 exhibited no acute necrotizing ulcerative gingivitis but were malnourished and 20 were free of acute necrotizing ulcerative gingivitis and in good nutritional state) were evaluated for the presence of viruses and oral microorganisms. The ANUG cases in the malnourished children had a higher incidence of Herpesviridae, the main virus being detected was cytomegalovirus. There were more anaerobic microorganisms recovered, with Prevotella intermedia as the predominant isolate, in the malnourished children as compared to the healthy children. A study of the predominant microflora in active sites of noma lesions was carried out in eight noma patients, 3-15 years of age, in Sokoto State, northwestern Nigeria. Fusobacterium necrophorum was recovered from 87.5% of the noma lesions. Oral microorganisms isolated included Prevotella intermedia, alpha-hemolytic streptococci and Actinomyces spp. which were isolated from 75.0, 50.0 and 37.5% of the patients, respectively. Peptostreptococcus micros, Veillonella parvula, Staphylococcus aureus and Pseudomonas spp. were each recovered from one lesion. All strains were observed to be sensitive to all of the antibiotics tested with the exception of one strain of P. intermedia which showed resistance to penicillin. The pathogenic mechanisms of F. necrophorum as a trigger organism were discussed. The isolation from human noma lesions of F. necrophorum, a pathogen primarily associated with animal diseases, may have important etiologic and animal transmission implications.