Anaerobic bacteria of the genus Pectinatus cause beer spoilage by producing off flavors and turbidity. In unpasteurized beer even a small initial amount of contamination is likely to lead to a defective product. Detection of Pectinatus by traditional microbiological techniques is time-consuming and not practical as a preventive product control measure. In this paper Pectinatus-specific primers capable of discriminating among other beer contaminants by polymerase chain reaction are described. The present procedure, which includes the isolation of DNA from the contaminated beer sample, the polymerase chain reaction, and the electrophoretic identification of the reaction products could be performed within 10 h. The detection level in inoculated beer samples was ca. 20 cells per ml. The technique therefore has a potential in routine product control.