Legionella feeleii has been implicated by serologic studies as the causative agent in an outbreak of Pontiac fever and has been recovered from an institutional water source. Pneumonia caused by this agent has not been described previously. The authors have isolated L. feeleii from two immunosuppressed patients with community-acquired pneumonia and from an institutional water source. One patient survived after treatment with erythromycin. The other patient was leukopenic and died of pneumonia. Isolates exhibited typical cultural and biochemical features of L. feeleii and reacted with L. feeleii serogroup 1 antiserum. L. feeleii serogroup 1 is now known to cause not only Pontiac fever but also pneumonia in humans.