A rapid method has been developed to determine enterococci using immunomagnetic separation and bioluminescence. Small paramagnetic beads are coated with antibodies having a specific affinity to enterococci. The captured enterococci are quantified by bioluminescence. The entire procedure takes 30 minutes without a pre-enrichment step. After developing the method, field tests were performed in California. Eight beach samples were provided for determining enterococci using the rapid method. At the same time, the same samples were tested with traditional methods performed by 26 local laboratories. The results show a significant agreement between the two methods. In six out of the eight locations, the predictions based upon the rapid method agreed well with the average values by the traditional methods in determining the quality of swimmable water. Among these, the four predictions were very close to the average colony count. The results also showed the sensitivity of the rapid method (<104 CFUs/100 ml).