A case of pneumonia due to Legionella bozemanii--only the 20th culture-proven case reported so far--progressed with cavitation 9 days after the initiation of intravenous therapy with erythromycin. Review of all 20 reported cases revealed a similar propensity toward radiographic progression (25%) and cavitation (25%) during therapy. A slow response to long courses of erythromycin was the rule (35% of cases). In two instances, long courses of intravenous erythromycin failed and the patient died. Pleural effusion was reported in 60% of patients, including two with empyema. Overall mortality was high (40%). Although mortality was only 21% among patients who lived long enough to receive adequate courses of erythromycin, all three such patients who died had received erythromycin alone. Combination therapy with erythromycin and rifampin proved more effective in terms of survival. Infections due to non-pneumophila Legionella may be overlooked because of the organisms' special serological and culture requirements.