Microflora of domestic water can be a source of active ooze adapted to sulphanilic acid. Adaptation of the microflora to sulphanilic acid at a concentration of 170-200 mg/l takes 6 to 8 days. The microflora of active ooze, immediately after adaptation, consists mainly of Pseudomonas species, Ps. denitrificans, Ps. fluorescens, Ps. striata, Ps. putida, etc., and also of Achromobacter stutzeri, Achromobacter flavum, Mycobacterium phlei, Mycobacterium mucosum, Bacillus mesentericus, Bac. cereus, saccharomyces cerevisiae, Schizosaccharomyces pombe, and Rhodotorula glutinus. The number of the species decreased as a result of long cultivation of active ooze on a minimal medium with sulphanilic acid as a sole source of carbon and nitrogen; the following strains prevailed: Ps. putida, Ps. eisenbergii, strains of Mycobacterium phlei and Flavobacterium solare. The isolated strains of Ps. putida and Ps. eisenbergii decomposed sulphanilic acid by 60.0--79.5 percent, and together with Mycobacterium phlei by 100 percent during 4 to 7 days. The ability to oxidize sulphanilic acid decreased after storage. Addition to the medium of other sources of carbon, nitrogen and vitamins did not restore the lost ability of the microorganisms to decompose sulphanilic acid.