In this issue, Klein and a cadre of epidemiologists, mycologists, and clinical and public health investigators describe the largest reported outbreak of acute blastomycosis with a known source; it involved persons attending an environmental camp on the Eagle River in Wisconsin.1 Klein et al. provide important new information about the epidemiology, pathogenesis, and diagnosis of blastomycosis, one of the important endemic systemic mycoses in North America. Earlier studies have characterized the morphologic and growth features of the causative dimorphic fungus, Blastomyces dermatitidis, as well as the clinical disease. Primary infection in humans takes place after inhalation of oval conidia…. © 1986, Massachusetts Medical Society. All rights reserved.