Eight adult patients from Port Elizabeth with significantly raised indirect fluorescent antibody titres of greater than or equal to 256 against the Legionnaires' disease bacterium are described. One of these patients had in addition elevated antibody levels against Mycoplasma pneumoniae. The clinical manifestations of the patients ranged from an 'influenza-like' illness in 1 patient to pneumonia of varying severity in 6. One patient had a severe illness with fever, couth and encephalopathy, together with the uncharacteristic features of lymphadenopathy and a petechial rash. This patient did not have pneumonia. Attention is drawn to unusual clinical aspects in some of the patients and the need for improved definitive diagnostic procedures is emphasized.