A disease causing increased mortality and abortion in domestic animals during a 1977 epizootic in Egypt was identified as Rift Valley fever (RVF) virus. The epizootic included extensive human involvement reflected clinically as either an acute febrile, ocular, encephalitic, or fatal haemorrhagic form of RVF disease. The virus was again isolated from humans and animals during a second RVF epizootic in the summer of 1978.