Two cases of Legionnaires' disease proven by seroconversion in indirect immunofluorescence are reported. Creatine phosphokinase (CPK) was increased in both patients, and one had rhabdomyolysis with acute renal failure and acute respiratory distress. A review of the literature brought out 9 other cases of rhabdomyolysis associated with Legionnaires' disease. Myalgias are an inconstant warning symptom; renal impairment is present in more than one half of the cases, and although pulmonary lesions are moderate, respiratory muscle involvement may require mechanical ventilation. In view of the severe complications of rhabdomyolysis, CPK should be systematically assayed in patients with Legionnaires' disease; 57 p. 100 of whom, according to published reports, have high CPK levels. In a retrospective study of bacterial pneumonia caused by common pathogens, we found that CPK was elevated in 31 p. 100 of the cases. The mechanism of muscular involvement is discussed.