Brucellosis is one of the neglected diseases in Nigeria. In Lagos, the commercial capital of Nigeria with about twenty one million people, a descriptive cross-sectional study was carried out in order to determine the sero-prevalence of brucellosis among people at risk in some selected abattoirs and secondary health care facilities (hospitals) in the state. Mixed sampling method was employed at the abattoir while convenient sampling method was used in sampling the respondents at the hospitals. Sera samples from three hundred and one (n=301) abattoir-based workers and traders; and one hundred and twenty one (n=121) hospital-based individuals which include people with febrile illnesses and blood donors were tested for brucellosis using Rose Bengal Plate test (RBPT), with indirect ELISA being used as a confirmatory test. Of the 301 abattoir-based workers and traders, 27 (8.97%) were sero-positive to the infection when Rose Bengal Plate test antigen was used. The twenty seven individuals consists of fifteen (15) butchers; four (4) veterinarians; two (2) meat transporters and bone/cow horn dealers each as well as one each of blood meal producer, abattoir engineer, water seller and meat supplier. When blood samples from the sero-positive individuals were subjected to ELISA, 3 (11.1%) were sero-positive to the brucellosis, while one is equivocal. These results confirm that agglutination observed on RBPT might be related to unknown cross-reactions and confirmation with a different test was necessary. None of the hospital-based respondents is sero-positive to the infection. The clinical signs significant for the infection in this study were fever, joint pain, lower backache, regular headache and miscarriage. Brucellosis awareness level among the respondents was very low. Data was analysed using (SPSS) version 20.0 at α0.05 significant level. The significant risk factors for human brucellosis according to this research are consumption of fura (unpasteurized milk) and wara (fresh cheese). The study revealed that brucellosis is not only an occupational disease but can also affect people who trade or live in proximity with infected animals. / Agriculture, Animal Health and Human Ecology / M. Sc. (Agriculture)