The microbiological quality of beer is generally assessed on the basis of culture detection. If microorganisms are detected using suitable media, morphological examinations, antibody techniques and/or PCR methods are performed to identify the microorganisms.Since this technique requires at least for several days for cultivation, a more rapid and accurate detection method for beer-spoilage bacteria has been desired. Over the past decade, the FISH (fluorescent in situ hybridization) method has made a rapid progress as a tool for the enumeration and the identification of the target bacteria, and has been widely applied to the environmental and clinical field. Last year in WBC2000, we showed that the DNA probes specific to Pectinatus species could successfully identify Pectinatus species in a species-specific manner, and detect Pectinatus among several thousands of non-Pectinatus cells at the single cell level. The FISH method has a great potential for direct quantitative detection of beer-spoilage bacteria without any culturing steps and the procedures can be completed within five hours. However the quantitative detection method we reported requires an extra step for recovering and washing cells by centrifugation and a considerable number of cells might be lost in this process. For this reason, the detection limit of this FISH method (10(^3) Pectinatus cells/100 ml beer) was significantly lower than we expected. This FISH method also has a possible risk of contamination during the procedures. In this study, we newly developed the direct detection method on a filter membrane using the probes conjugated with fluorescent dye. We had to overcome three technical problems to detect target bacteria on a membrane by FISH. (1) fixing bacteria quickly and efficiently on a membrane, (2) keeping the membrane soaked with probe-solution in a dark closed system during hybridization, (3) increasing fluorescence intensity of target bacteria. Using beer-samples containing approximately 10 cells of Pectinatus, we succeeded in detecting the target bacteria on a membrane by FISH. The sensitivity of this method was evaluated by comparing with a traditional cultivation method. In this presentation, we will discuss the potential application of this method to microbiological quality control of beer and work-in-process products.