An outbreak of Venezuelan equine encephalomyelitis (VEE) virus infection occurred in seven of a 24-man unit of U.S. soldiers engaged in jungle survival training in the Canal Zone. The illness was characterized by sudden onset of fever, intense headache, generalized muscular and joint pains, and leukopenia. Transient signs of encephalitis occurred in only one man. VEE virus was isolated from the serum of each of the affected men, and all developed specific, neutralizing antibodies during convalescence. Epidemiologic evidence strongly suggested that the disease was acquired at a single campsite, with a high incidence of infection among men bivouacked in a small area of that site. VEE virus was isolated from two of five sentinel hamsters exposed in the camp 1 month later, suggesting that the outbreak resulted from contact with a localized area of endemic virus activity.