The microbiological laboratory can assist in diagnosis and therapy of bacterial endocarditis with the following parameters: cultivation and identification of the causative organism, sensitivity testing including assessment of the minimal bactericidal concentration (MBC) and testing of antibiotic combinations with checkerboard titrations and time-kill curves. Serum bactericidal titers, although controversial with respect to their utility in prognosing the clinical outcome, are regarded useful by some authorities but not by others. Antibiotic assays, mainly for aminoglycosides and vancomycin, serve to monitor antibiotic serum levels.