In Egypt, bovine virus diarrhoea-mucosal disease (BVD-MD) was initially detected as the result of a serological survey of cattle and sheep, using the serum neutralisation test. In 1970, the causal pestivirus was isolated from bovine calves and buffalo calves with pneumonia and enteritis. Mixed viral infections were also prevalent. Cases of immune tolerance were identified. The Egyptian industry had complained of unthrifty cattle and high death rates of bovine calves and buffalo calves. A rinderpest outbreak in 1982 involved some cattle and buffalo which had been vaccinated against the disease, and such animals were positive to the gel diffusion test for BVD-MD pestivirus. Extensive immunosuppression due to BVD MD virus was suspected, because the attenuated cell-culture vaccine against rinderpest, issued in Egypt since 1965, had not been tested for freedom from non-cytopathic BVD-MD virus. Experimental infection of susceptible sheep with BVD-MD virus resulted in symptoms of Border disease. Innocuity of the attenuated C24V bovine pestivirus vaccine for animal tissues and the immune system of calves was confirmed.