The performance of a biphasic system for blood culture and a non-radiometric system using infrared spectroscopy was compared using 2,000 blood samples. The biphasic system detected bacteria or fungi in 237 blood cultures in 114 patients, while the non-radiometric system detected these microorganisms in only 186 blood cultures in 91 patients (p less than or equal to 0.05). The speed with which the bacteria were detected and the rate of contamination were similar in the two systems. The capacity to detect different genera and species was similar except in the case of Brucella spp., which the biphasic system detected in 28 blood cultures but the non-radiometric system in only 12 (p less than or equal to 0.05).