Abstract: A method for detecting low levels of microbial cells in samples of fluids and degraded solids. The non-microbial reactive materials in a sample are solubilized by selective use of enzymes and the sample is filtered to remove the liquid portion of the solubilized materials while retaining the microbial cells on the filter. The microbial cells are then ruptured to expose undiluted reactive material which is then contacted with reagent material on the filter to cause a luminescent reaction. The strength of the resulting luminescence is measured as an indication of the concentration of microbial cells in the sample.