Several reports have been published implicating Chaetomium spp. as opportunistic pathogens. A critical review of these cases was made, and the majority of the responsible strains were studied. Chaetomium globosum was the most common species, being isolated in at least nine clinical cases of infection. Some of these clinical isolates and others from environmental sources were tested against six antifungal agents (5-fluorocytosine, fluconazole, amphotericin B, itraconazole, ketoconazole and miconazole). The 23 strains tested were totally resistant to the first two drugs, and none of the other antifungal agents demonstrated fungicidal activity. There were no significant differences between the susceptibility of the clinical strains and the other strains.