The prevention of hamster-associated outbreaks of lymphocytic choriomeningitis virus infection in human beings requires rapid and reliable testing of large numbers of hamsters for the infection. To select the most effective test, the antibody response of infected hamsters was determined by the indirect fluorescent antibody and complement-fixation techniques. The indirect fluorescent antibody technique required less than 2 hours to complete, was the first to become positive after infection, and remained positive for at least several months. Infection in hamsters was also readily detected by the inoculation of mice with infected hamster tissues; virus could be isolated from several organs as early as postinoculation day (PID) 3, and all organs tested contained high concentrations of virus by PID 5. After PID 40, virus was detectable only in the kidney; this organ remained positive for over 3 months.