The value of determining D-lactate concentrations in body fluids for the rapid diagnosis of bacterial infections was investigated. A total of 336 body fluid samples were analyzed: 208 ascitic fluids, 57 synovial fluids, 40 cerebrospinal fluids and 32 pleural fluids. Using a cut-off value of 0.05 mM, the overall sensitivity was 0.96 and the specificity was 0.88. Therefore, the measurement of D-lactate concentration in body fluids offers a rapid (2-hour) and useful method of differentiating between infectious and non-infectious body fluid diseases.