The present study addresses the specificity of lytic osseous impact for distinguishing among metastatic cancer, tuberculosis, and fungal disease. Osseous impact is used in this manuscript as a convention to describe the macroscopic appearance of defleshed bones affected by the disease. Osseous changes in the skeleton of a 47-year-old black male, diagnosed in life as having blastomycosis, were characterized and compared to lytic lesions observed in ten individuals with tuberculosis and six with metastatic cancer in the Terry and Hamman-Todd Collections. Apparent distinguishing characteristics are identified. Eroded areas, present as fronts of resorption or the result of space-occupying masses in blastomycosis, with protruding, short, blunt, 1 x 2 mm spicules of new bone, are surrounded by periosteal reaction. These differed from smooth zones of resorption and coalesced lesions, with a smoothed marginal zone and space-occupied appearance--bone-displacing mass--in tuberculosis and lytic (nonpermeative) lesions of metastatic cancer. Displacing is a convention (an artificial term) denoting bone resorption and reformation at the outer edge of the tumor mass, giving the impression that the surrounding bone had expanded beyond its original margins. Irregular trabeculae are occasionally preserved in the margins, but remodeling in the form of blunting of those trabeculae is not observed macroscopically in either tuberculosis or metastatic cancer. Two apparently specific lesion types are noted in blastomycosis. Periosteal reaction surrounding fronts of resorption appears specific, at least for nonarticular osseous lytic lesions, among the three entities studied. Remodeling of isolated internal trabeculae in the space-occupying mass lesions of blastomycosis also appears unique among the three disorders studied. Comparison with coccidioidomycosis suggests that extrapolation of blastomycosis findings to other fungal diseases is feasible; description of additional clinically diagnosed cases is awaited.