The microbiological quality of 136 samples of bottled uncarbonated mineral water, including 88 domestic and 48 imported samples, was investigated. The numbers of samples with heterotrophic plate count (HPC) over the maximum level legally permitted in Taiwan (200 colony forming units ml-1) were 45 (51.1%) and 29 (60.4%) for domestic and imported samples, respectively. Coliforms and faecal streptococci were not detectable in the samples tested. Two of the domestic samples were contaminated with Aeromonas hydrophila and four with Pseudomonas aeruginosa. Bacteria isolated from water samples were identified as species of Pseudomonas, Aeromonas, Flavobacterium, Pasteurella, Xanthomonas, and Staphylococcus. Mold and yeast were detected in 38.6% and 18.8% of domestic and imported samples, respectively. The HPC of bottled mineral water stored at 25 degrees C increased quickly to 10(4)-10(5) colony forming units ml-1. In inoculation studies both A. hydrophila and Escherichia coli grew very well and mutualistic growth for both organisms was observed in mineral water at 25 degrees C.