Serum samples of 107 dentists, dental assistants, and dental technicians, working in practices or out-patient clinics, were examined with an indirect immunofluorescence test for antibodies to Legionella pneumophila (SG1-SG6, polyvalent). Serum samples of 106 non-medical workers served as a control. Thirty-six (34%) employees of the dental personnel from 13 practices showed a positive reaction, 24 of these had a weakly reactive titer of 1:32 to 1:64 and 12 a higher titer of 1:128 to 1:256. Dentists had the highest prevalence (50%) of L. pneumophila antibodies, followed by assistants (38%) and technicians (20%). Only 5 samples (5%) from the control group were positive (4 between 1:32 and 1:64, 1 at 1:256). Antibodies could be demonstrated in the dental personnel only after a 1.5-year period of employment ("exposition time"). These results indicate that dentists and dental personnel are at an increased risk of legionella infection.