Isolated reports of brucellosis among family members have been documented. The aim of this study is to determine if active serological screening of the households' members of acute brucellosis cases will detect additional unrecognized cases. From May 2000 to October 2001, patients with acute brucellosis were enrolled and their household members were serologically screened for brucellosis using the Standard Agglutination Test (SAT). Fifty-five index cases with acute brucellosis and 404 household members were enrolled. The majority of index cases (48%) were young adults, and 79% were illiterate. Ownership of animals and ingestion of unpasteurized raw milk were reported by 45 and 75% of the index cases respectively. Of the 55 families screened, 23 (42%) had two family members or more with serological evidence of brucellosis and 32 (58%) had only the index case. Households of > or = 5 members and a history of raw-milk ingestion by family members were risk factors associated with the seropositives (P < 0.05). Of the 404 household members screened, 53 (13%) were seropositive; of these 39 (74%) were symptomatic, and 9 (35%) had brucella bacteraemia. Symptomatic seropositives tended to have bacteraemia and higher brucella antibody titres compared to asymptomatic seropositives (P < or = 0.05). Screening family members of an index case of acute brucellosis will detect additional cases.