The method consists in inoculation of three tubes of double-strength liquid selective culture medium and of three tubes of single-strength liquid culture medium with a specified test sample. Then, under the same conditions, inoculation of further tubes with decimal diltutions of the test sample. Then incubation of the tubes at 30 °C for 24 h or 48 h, and examination of the tubes. After further treatments, calculation of the number of coliforms per millilitre or per gram, from the number of tubes in which gas formation has been noted. An annex A shows a diagram of procedure. Annexes B and C give tables forthe determination of MPN index.