The Cape mountain zebra (Equus zebra zebra) is one of the rarest species of mammals in South Africa, and is threatened with extinction. At present there are less than 200 in existence, of which approximately 160 occur in the Mountain Zebra National Park near Cradock. Because of the rarity of the species and the undesirable concentration of the majority in an area of only 6 536 ha, a post-mortem examination is performed, if possible, on all animals to establish cause of death with the purpose of preventing large-scale mortalities. This is done even if the carcass is in a fairly advanced state of decomposition. Amongst the examinations so performed were two zebra which were believed to have died as a result of intraventricular thrombosis. The rarity of this condition and of the Cape mountain zebra makes a report on these cases necessary.