Enzymatic hydrolysis of fluorogenic substrates (4-methylumbelliferyl-β-D-galactoside, 4-methylumbelliferyl-β-D-glucoronide) has been used for rapid (25min) detection of indicators of faecal water pollution, i.e. coliform and thermotolerant coliform bacteria. In the present work, enzymatic activities and different groups of bacteria (i.e. thermotolerant coliforms, coliforms, β-ga1actosidase positive and β-glucuronidase positive bacteria) from sewage effluent and polluted river water have been investigated. Ratios of the order of 1:10 between coliforms and β-galactosidase positive bacteria were demonstrated. The contribution from β-ga1actosidase positive non-coliform bacteria to the measured enzyme activity should not, therefore, be neglected. Numbers of β-glucuronidase positive non-coliforms indicate interference of this group in the rapid assay.