Water samples were collected from the hot water systems and from dental units in 12 dental offices of Dresden and cultured for legionellae. From seven (58%) hot water supplies and from dental units in 6 (50%) offices legionellae could be isolated. To asses the hygienic risk for dental staff we studied the prevalence of antibodies against Legionellae in serum samples of 113 dentists, 105 dental nurses and 17 dental technicians. In comparison with a control group of healthy people (132 women, 161 men, 20-80 years) living in the Dresden area, dentists have had a higher prevalence of antibodies against legionellae. In a lesser degree this was the case in sera of dental nurses and dental technicians. There were substantially differences in the prevalence of legionellae antibodies in different facilities. The incidence of positive antibody titers rises with the duration of occupation. None of the dentists with high antibody titers have had a story of pneumonia in their history of life. Thus a higher risk for dentists to acquire legionnaires' disease during their professional duty cannot be established.