Interest in rapid bacterial detection methods for sanitary indicator bacteria in water prompted a study of the use of [U-14C]mannitol to detect fecal coliforms (FC). A simple method which used m-FC broth, membrane filtration, and two-temperature incubation (35 degrees C for 2 h followed by 44.5 degrees C for 2.5 h) was developed. [U-14C]mannitol was added to the medium, and the temperature was raised to 44.5 degrees C after 2 h at 35 degrees C. 14CO2 was collected as Ba14CO3 and assayed by liquid scintillation spectroscopy. Correlations were examined between FC cell numbers at the start of incubation (standard 24-h FC test) and Ba14CO3 counts per minute after 4.5 h. Results indicated that FC numbers ranging from 1 x 10(1) to 2.1 x 10(5) cells could be detected in 4.5 h. Within-sample reproducibility at all cell concentrations was good, but sample-to-sample reproducibility was variable. Comparisons between m-FC broth and m-FC broth modified by substituting D-mannitol for lactose indicated that the standard m-FC broth was the better test medium. Results from experiments in which dimethyl sulfoxide was used to increase permeability of FC to [U-14C]mannitol indicated no increase in 14CO2 production due to dimethyl sulfoxide. Detection of FC by this method may be useful for rapid estimation of FC levels in freshwater recreational areas, for estimating the quality of potable source water, and potentially for emergency testing of potable water, suspected of contamination due to distribution line breaks or cross-connections.