['Lactic acid concentrations (LA) are an established marker of bacterial infection in cerebrospinal fluid (CSF). However, use of LA for the detection of infection in CSF with residual blood has not been fully evaluated.', 'Analysis of LA and total protein, cell count and bacterial culture were performed in 90 lumbar and ventricular CSF samples contaminated with blood.', 'Bacterial culture was positive in six CSF samples. The diagnostic value of the cell count was significantly higher than that of LA for the prediction of a positive culture, even if all culture positive and all likely infected samples were included in the analysis. There was no significant difference in LA concentrations between positive or likely positive ventricular CSF samples and all negative, ventricular samples.'] Is lactic acid of low predictive value for the diagnosis of bacterial infection in ventricular cerebrospinal fluid samples containing residual blood?