Bolivian hemorrhagic fever (BHF) was first recognized in the Province of Beni, Bolivia, in 1959 (1), and cases have continued to occur since then. Recent outbreaks have confirmed the fact that clinical manifestations can be quite nonspecific. Laboratory diagnosis is handicapped by a scarcity of facilities in the endemic region, as well as by the hazard to nonimmune personnel of working with the causative agent, Machupo virus. These problems also apply in varying degree to two other diseases caused by members of the arenavirus group (2, 3): Argentine hemorrhagic fever (AHF) caused by Junin virus (4) and Lassa fever caused by Lassa virus (5). The early recognition of outbreaks of these diseases is important since rodent control, immune serum therapy, and isolation of patients are thought to be of some use in treatment and prevention.A plaque-neutralization test for detection of Machupo virus antibodies has been developed and proved to be specific and sensitive (6). However, these advantages are posited on t...