The aims of this study were to assess community knowledge, awareness and practices on zoonoses, to gather baseline data on brucellosis in livestock and wildlife, to establish brucellosis seroprevalence in domestic ruminants and humans and risk factors associated with livestock seropositivity, to assess brucellosis dynamics and impact on livestock production and reproduction and to evaluate the performance of the Rose Bengal Plate Test (RBPT) in Tanzania. The results described in this study were carried out through Participatory Rural Appraisal (PRA), cross-sectional and longitudinal studies. In the PRA and cross-sectional studies, rabies, tuberculosis, anthrax and brucellosis were the zoonoses most frequently identified. Cattle were frequently identified as being associated with tuberculosis, anthrax and brucellosis, whereas dogs were frequently identified as being associated with rabies. Small ruminants, pigs, cats and poultry were either infrequently, or not identified as being associated with zoonoses. Recognition of clinical signs of zoonoses in humans was better than in animals. Ingestion of animal products was a route frequently identified as transmitting zoonoses to humans. During the baseline serosurvey, seroprevalences for brucellosis were 6.2% in cattle, 6.5% in small ruminants and 13% in wildlife, respectively. Seropositivity was significantly higher in the pastoral (13.2%), followed by agro-pastoral (5.3%), and lowest in the small holder dairy system (2.3%) (p<O.05). During the cross-sectional serosurvey, the seroprevalence was significantly higher in older animals and large herds (p<O.OOl). Variation in seropositivity between households was higher (1-30%) in the pastoral compared to agro-pastoral (1-14%) households. The model that best explained c-ELISA seropositivity included the feeding of dogs with foetuses and placentae, calving during the wet season, and the fanning system. In humans, 28% of families were seropositive for brucellosis with the highest levels in Ngorongoro district (46%), and lowest in Babati district (0%). Families with seropositive herds were 3.3 times more likely to be seropositive. However, 25% of families were seronegative when their herds were seropositive, and 48% of families were seropositive with seronegative herds. In the longitudinal study, the incidence was 73211,000 cases per animal-years at risk with an estimated survival probability of 0.836. Households with a high seroprevalence at the initial sampling had a high incidence of seroconversion in the subsequent visits. Occurrence of new seropositive cases was significantly higher in the wet season (p< 0.05). Calf serostatus was statistically associated with dam serostatus but no significant difference in growth rate was observed between calves suckled from seropositive and seronegative dams. Brucella melitensis type-1 was isolated from goats' milk following culture. Blood and placenta samples were negative on bacteriological culture. The RBPT was found to have low sensitivity in both field and laboratory settings. Brucellosis infection in livestock is widespread, but poses the greatest risk to human health and livestock production in pastoral systems in Tanzania.