Malignant catarrhal fever (MCF) is defined as a clinicopathological syndrome caused by related herpesviruses and acquired from persistently infected wildebeest and sheep. There is convincing epidemiologic and virologic evidence that Alcelaphine herpesvirus 1 (AHV1) causes the wildebeest-derived disease (WD-MCF). Present knowledge suggests that a herpesvirus related to AHV1 may be associated with some cases of the non-wildebeest-associated disease (NWA-MCF). However, this virus possibly represents a passenger virus not related with the ultimate cause of the disease. Moreover, evidence for the role played by sheep as the reservoir for the agent of NWA-MCF is not convincing and awaits confirmation.