There are more than 100000 recognized species of fungi, comprising 25% of the biomass of the earth. Allergic, IgE-induced, manifestations of airborne fungi are common, whereas non-IgE manifestations are rare. Recently, much focus has been placed on the non-IgE-mediated effects of various molds, including hypersensitivity pneumonitis, infectious disease, and mycotoxicoses. Hypersensitivity pneumonitis is a clinical syndrome associated with systemic and interstitial lung disease that occurs in susceptible individuals following fungal inhalation. Most fungi are not pathogenic to man; however, certain fungi are capable of infecting immunocompetent individuals. Although mycotoxins and exposure to mycotoxins ("toxic mold syndrome") are implicated in causing numerous, nonspecific, systemic symptoms, currently, there is no scientific evidence to support the allegation that human health is affected by inhaled mycotoxins. However, if mold is discovered in a home, school, or office setting, the source should be investigated and appropriate remediation undertaken to minimize structural damage and potential allergic sensitization.