The AIDS epidemic has led to the resurgence of tuberculosis. Extrapulmonary manifestations may appear in over half of the patients who are dually infected. This has resulted in a rising incidence of tuberculous pericarditis in several parts of Africa such as Tanzania. We tested a solid-phase antibody competition sandwich ELISA (SACT-SE) as a potential means of diagnosing tuberculous pericarditis. Fifty-one African patients with clinically diagnosed tuberculous pericardial effusion (of whom 25 had confirmation by pericardial fluid culture) were tested using a monoclonal antibody (CDC/WHO ref. no. IT39) which was raised against a specific epitope on the Mycobacterium tuberculosis 30 kDa antigen. All but one patient had negative sputum microscopy for acid-fast bacilli. A sensitivity of 61% (at 96% specificity) was achieved. Sera from 25 African patients with smear-positive tuberculosis were also examined; of which 20 tested positive (sensitivity 80%). This is the largest study to date on the potential application of serology in diagnosing pericardial tuberculosis.