Potable water specimens, usually well water, were analyzed for total and fecal coliforms by a Standard Methods membrane filtration test (MF) and the Colilert Presence/Absence test (CPA), Access Analytical, Inc., Branford, CT. MF sample membrane filters were incubated on M-Endo agar plates at 35°C for 22 to 24 hours. Positive colonies were subcultured to Brilliant Green Bile Broth (BGB) and Lauryl Tryptose Broth (LTB) to confirm total coliforms by gas production and to EC medium (EC) incubated at 44.5°C to verify fecal coliforms. The CPA test consisted of the addition of a dehydrated powder containing salts, 4-methylumbelliferyl-B-D-glucuronide (MUG) and O-nitrophenyl-B-D-galactoside (ONPG) to 100 ml sample followed by incubation at 35°C for 24 hours, visual reading for ONPG hydrolysis (total coliforms) and under long wave UV light for MUG hydrolysis (Escherichia coli). When positive result was obtained from either system, the predominant organism was recovered and identified by the API 20E system (Analytab Products, Inc., Plainview, NY). In this study, the results of the Colilert total coliform test (ONPG hydrolysis) were compared to the total coliform results of the MF test and the E. coli (MUG hydrolysis) result by Colilert were compared to fecal coliform results by the MF test. A total of 271 paired samples were analyzed with 93.7% agreement. Two hundred and twenty samples were negative by both procedures. Thirty three samples were positive by both procedures for total coliforms (28) and fecal coliforms (5). Discordant results were obtained for 18 samples (6.7%). The MF procedure detected total coliforms, not detected by the CPA in 6 samples. CPA detected total coliforms in seven samples not detected by MF. Standard Methods membrane filter test obtained positive results for both total and fecal coliforms in three samples where CPA only detected total coliforms and was positive for one sample each for both total and fecal coliform while CPA was negative for both. CPA was positive for total and fecal coliforms for one sample in which the standard method was positive only for total coliforms.