Tuberculous meningitis still poses a major diagnostic problem. Recently, several new techniques for rapid diagnosis of tuberculous meningitis have been developed. One of these newer techniques is the detection of mycobacterial fatty acids, using gas chromatography--mass spectroscopy. In this study we evaluated the sensitivity and specificity of this recently reported method in a blind trial. The sensitivity was found to be 100%, specificity only 91%. The number of false positive results limits the value of this test in the primary diagnosis of tuberculous meningitis. Nonetheless, we consider this method to be a valuable tool for establishing the diagnosis in culture-negative patients presenting with signs and symptoms suggestive of tuberculous meningitis.