Four patients with visceral infections due to the fungus Petriellidium boydii, who were recently hospitalized in our institutions, are described. Three of the patients were compromised hosts; in the fourth patient, infection occurred after trauma. All had received prior steroid and antibiotic therapy. Studies of patients with mycetoma or secondary infection of a pulmonary cavity due to this organism and of patients with visceral infections are reviewed. Because of histologic similarities to Aspergillus species, infections due to P. boydii may have been misdiagnosed in the past if the infecting fungus was not isolated in culture. The fungus has been shown to be resistant in vitro to currently available antifungal agents. Resistance to amphotericin and 5-fluorocytosine is demonstrated in our studies. There are few reports of successful chemotherapy of any manifestation of this infection, and no such reports of visceral disease. We demonstrate in vitro sensitivity of isolates in our cases and in others to micronazole, a new antimicrobial agent; this drug may be indicated for treatment of disease due to P. boydii.