The rules of the European Economic Community to harmonize the hygienic quality of drinking water write out the faecal streptococci as indicator organisms. This operating definition of the faecal streptococci prohibits its taxonomic limitation to enterococci or group D streptococci. Therefore, we have undertaken studies concerning the methods for routine examinations. Comparative investigations of selective enrichment broths showed no significant differences of the end concentration of glucose in the range of 0.5-1.0% and of sodium azide in the range of 0.02-0.05%. 36 degrees C was a better incubation temperature than 44 degrees C and the results were better after 24 h than after 48 h. Comparative investigations of selective plating media showed less selectivity of the bile-aesculin agar and gentamicinthallous-carbonate agar than that on the one hand of citrate-azide-tween-carbonate agar, KF streptococcal agar or Slanetz-Bartley enterococcal agar, and on the other hand of kanamycin-aesculin-azide agar. All together the kanamycin-aesculin-azide agar seems to be a little better than the other media (Table 2) 356 strains of faecal streptococci were isolated from the studied media. More than 20 characteristics were investigated and, there upon, the strains were differentiated (Table 3). S. faecalis predominates in human materials, i.e. urine, S. faecium and S. durans were isolated specially from sewage and waste water (Table 4). The single species of faecal streptococci grow specificly on the different selective media, and therefore, each agar specimen prefers the one or other species more or less selectively (Table 5).