Coccidioides immitis is a dimorphic fungus that grows as a filamentous mold
in soil and as a spherule at human body temperature. The hyphal or soil fo
rm is found rarely in human tissue. We report 5 cases of coccidioidomycosis
in which hyphae were found in brain tissue or spinal fluid, The presence o
f central nervous system plastic devices appears to be associated with morp
hological reversion to the saprophytic form. This reversion has implication
s for diagnosis and therapy and may increase the risk of obstruction of the
device(s).