A mmimum of one day is usually required to determine the presence of bacterial growth in blood cultures. We have developed a method for the detection of bacterial growth in blood cultures that is fast, objective, and sensitive. It is based on the incubation of the cultures in liquid media to which 14C-glucose has been added as the sole source of carbohydrate. The evolution of HC-dioxide is measured as an index of bacterial growth. Method 14C02 released by the bacterial metabolism of HC-labeled glucose is measured continuously with a commercially available monitor for radioactive gas. An air pump flushes the ionization chamber of this instrument at a rate of 9.5 liters per minute. The reaction flask is connected by means of Tygon tubing to form a closed system (Fig. 1). To record the radioactivity in the perfused gas, an analogue recorder is connected to the ionization chamber. The lower limit of sensitivity of this instrument is 0.0036 µCi of 14C (1). The culture medium was 20 ml of glucose-free thioglych...