Recent work established the fact that the portal of entry in blastomycosis is the lung. After the initial exposure to the fungus, a pneumonic process develops that may heal spontaneously or progress locally or at distant sites, or both. Frequently, however, patients present with disseminated disease, whose chest roentgenograms do not show any lesions. We have recently seen three patients with disseminated blastomycosis with negative chest roentgenograms at the time of diagnosis. Past history showed a pneumonic illness 33, 32, and 4 months before diagnosis. Chest roentgenograms from the time of the original illness showed a pneumonic process compatible with blastomycosis in all three. Examination of postbronchoscopy sputa showed the characteristic yeasts of Blastomyces dermatitidis. These three patients document for the first time apparent endogenous activation in blastomycosis. A possible explanation for this apparent endogenous activation may reside in the histopathologic similarity between blastomycosis and other chronic granulomatous diseases, especially tuberculosis.