The diagnosis of fungal infections of the respiratory tract is often difficult and may require invasive diagnostic procedures. The detection of soluble fungal antigens in bodily fluids such as serum, pleural fluid, and bronchoalveolar lavage fluid may substantially improve the ability to diagnose fungal respiratory diseases. For instance, uncommon presentations of diseases with the pathogenic fungi, such as chronic cavitary histoplasmosis, coccidioidal empyema, and cryptococcal pneumonia are often difficult to diagnose with present techniques, and the detection of fungal antigens may prove to be more sensitive. There is an especially urgent need for sensitive, reliable, commercially available tests for the diagnosis of opportunistic fungal pneumonias that occur in immunocompromised hosts. Preliminary data holds promise for the noninvasive diagnosis of deep-seated candidiasis (including pneumonia) and pulmonary aspergillosis by the detection of fungal antigens in serum and bronchoalveolar lavage fluid. We review current techniques used for the detection of fungal antigens, including their sensitivity and specificity, and their use in diagnosing human infections.