Summary
In the present work, a natural epizootic caused by Cordyceps unilateralis (Tuslane) Saccardo, in Camponotus sp adults was detected. It occurred in a tropical rain forest at km 45 Manaus-Boa Vista highway, State of Amazonas, Brazil (2°26' S, 60°02' W), In July 1977. About 3,500 Infected ants were collected. The morphology of sclerotium and stromata is described, and their mean dimensions are given. Some features of transmission are analysed. Attempts to produce the perfect stage on three artificial media were unsuccessful. The significant natural occurrence of Cordyceps unilateralis in populations of Atta cephalotes, suggests that more studies on the ecological requeriments of this fungs, might be realized in microbial control projects of this agricultural pest, in Brazil.