In 1967 an apparently new viral hemorrhagic disease appeared in research workers in the cities of Marburg and Frankfurt in West Germany, and in Belgrade in Yugoslavia. In all, 35 workers became ill, of whom 9 died. The only common factor between the three centers was a batch of green monkeys, imported from Uganda. These animals had been used throughout the world to provide tissue cultures with up to 12,000 being imported annually into the USA, with no previous disease noted. Eventually a virus was isolated and called the Marburg virus, but as yet it has not been detected to give any symptoms in the monkeys.