An impedance technique is presented as a method which offers promise as a test for estimating the numbers of total coliform bacteria in wastewaters. The technique reported here has the advantage of being 3-4 times faster than the standard membrane filter method (i.e. 4-7 h, compared with 20-24 h). The technique shows the disadvantages of (a) being markedly higher in initial cost of instrumentation, (b) being somewhat more expensive in required supplies, and (c) giving results which deviate considerably from the values given by the MF method. A parallel use of the impedance and MF methods when both speed and accuracy are desired may be an appropriate practical compromise.