Summary In the late summer of 1967 an epidemic in thirty-one patients in Germany and Yugoslavia of a disease transmitted from African green monkeys occurred; seven patients died. The incubation period was from 4 to 7 days. The main clinical features were headache, high fever, diarrhoea, a very characteristic rash, severe bleeding tendency and involvement of the central nervous system. Nearly all organs were involved and showed severe cell necroses. The aetiological agent was identified as an RNS-virus and was named Marburg virus. It was detected in the blood, urine, throat-washing and seminal fluid.