Abstract: A method for determining the number of microorganisms in a liquid sample, including the steps of dividing the liquid sample into a plurality of separate sub-samples, measuring the magnitude of at least one impedance component across each of the sub-samples and determining the number of the sub-samples for which the measured magnitude of the at least one impedance component indicates microorganism growth. The method preferably further includes the steps of applying A.C. voltage at a plurality of frequencies across at least a portion of the sample and measuring the at least one impedance component in response to at least some of the plurality of A.C. frequencies.