Nocardia asteroides, the most commonly recognized aerobic actinomycete, causes significant disease in immunocompromised patients. Clinical presentations can include pneumonia, skin abscess, bacteremia, brain abscess, eye infection, and joint infection. Other species associated with human disease include Nocardia brasiliensis, Nocardia otitidiscaviarum, Nocardia farcinica, Nocardia nova, and Nocardia transvalensis. Cryptosporidium and Isospora species have been identified as causes of severe diarrhea in immunocompromised hosts, but they can also cause diarrhea in the immunocompetent host. Oocysts in clinical specimens may be difficult to identify with out special staining.