Two approaches have recently been proposed for rapid detection of E. coli using the ChemScan method. The first one is based on in situ hydridization using peptic nucleic (PNA) probes[10], the second one demonstrates B-glucuronidase activity in both single cells and small microcolonies using a two-stage enzymatic labelling procedure (8,9). In this approach, growth/enzyme induction is separated from the actual labelling yielding optimal enzyme induction in the first and a rapid substrate turnover in the second step. Both tests take 3.5 h to complete. The ChemScan E. coli method was applied in the daily routine testing of tap water, partially purified water as well as water taken in emergency situations. Raw and well water samples were analyzed to obtain a sufficient number of positive responses for calculation of equivalence with reference methods. Includes 16 references, tables.