Summary.A double layer plating technique was used for countingBdellovibrio bacteriovorusin river water and sewage samples. The optimum conditions for enumeration were provided by dilute media with 0.6 % of agar as the top layer, incubated for 6 days at 30° withAchromobactersp. as the host. Pretreatment of samples affected counts: centrifugation and membrane filtration reduced the bdellovibrio count, homogenization increased it. Protozoa in sewage samples caused large plaques that greatly hindered counting and attempts to eliminate these plaques were unsuccessful. The highest counts in sewage samples averaged 900 cells/ml