In detecting pathogeuic viruses in water sample, polymerase-chain-reaction (PCR) amplification was uscd. In order lo obtain the intact viral particlc, five concentration techniques were compared and an improved procedure was developed with some modifications. Among them, adsorption-elution~EG precipitation and flocculatio~~iultracentriEugation were more efficient than others with thc detection limit of 10 PFU $ml^{-1}$. By the additional step removing inhibitory compounds for PCR reaction, the purity of the concentrated sample was improved and the detection limit was lowered by one order (to 1 PFU $ml^{-1}$. To examine the availability of the optimized procedure for field surveys, the distributions of enterovirus in Han River were estimated using the novel procedure. Seventy-five percentage (618) of sewagc samples and twenty percentage (2110) of river water samples were positive for enterovirus. These results indicate that adsorption-elutionPEG precipitation by PCR method is useful for the prompt and handy monitoring of viral contaminaiton in water environment and pathogenic viruses are widely distributed in water environments of Seoul.