We used the biotyping scheme using carbohydrate substrate utilization test with 14 carbon sources to speciate Acinetobacter isolates from blood and cerebrospinal fluid cultures of patients admitted to the postoperative neurosurgery ICU during January to November 1996. Sixty one patients culture positive for Acinetobacter sp. from blood or cerebrospinal fluid were followed up prospectively. Among these patients, 40 patients had clinically diagnosed infections like bacteriemia or meningitis while in 21 patients the isolation was regarded as contaminants. A. baumanniii was the most common isolate associated with clinical infections while A. lwoffii was more likely to be an environmental contaminant.