Over a period of 3 years, Legionella pneumophila serogroup 6 strains were isolated from warm water outlets and dental units in the Dental Faculty and from the Surgery and Internal Medicine Clinics at the University * Corresponding author. serogroup 6 strains isolated during a 3-year surveillance from a water system at the School of Medicine in Dresden, Germany. MATERIALS AND METHODS Water samples. After at least 16 h of stagnation, 0.3to 0.5-liter water samples were collected from dental units and warm water taps in the Faculty of Dentistry, School of Medicine in Dresden over a 3-year period. In the Internal Medicine Clinic, Surgery Clinic, and the bacteriological unit, warm water specimens from taps and faucets were sampled once in the same manner. The four facilities mentioned above are separate buildings, connected with a ring pipe warm water system. This water system is fed by two separate hot water tanks, which were employed one after the other. The temperature in these tanks was adjusted to between 56 and 58°C. During this study, no measures for eliminating legionellae such as superheating to 70°C or chlorination were made. The water temperature in the warm water system ranged from 30 to 50°C at the time of water collection. Legionella strains and culture conditions. Water samples were concentrated by centrifugation at 5,500 x g for 30 min. Legionellae were isolated on ACES [N-(2-acetamido)-2aminoethanesulfonic acid]-buffered charcoal-yeast extract (BCYE) agar medium (4, 8) supplemented with 0.1% ox-ketoglutarate (Sigma Corp.