Since the coliform group of organisms were adopted as indicators of water pollution, numerous laboratory tests have been devised to determine the presence or absence of these organisms. Coliforms in water supplies, surface waters or sewage effluents can be quantified by the multiple tube (MPN) or membrane filter (MF) techniques. The MPN procedure has been used by sanitary engineers for over 50 years. The MF technique, while experimentally more attractive, has yet to prove its usefulness, reliability and ruggedness over the extremes met by the MPN method. The reliability and constraints on the methods were assessed. It is concluded that: (1) over all sample types the MPN and MF techniques are statistically comparable; (2) these techniques measure different biological populations of fecal or total coliforms; (3) for a given type of sample, e.g., fecal coliforms in a chlorinated effluent, the techniques are statistically different; (4) the precision of the MF method is four times better than that of the MPN technique.