The diagnosis of both bovine viral diarrhoea (BVD) and mucosal disease (MD) is usually made on the basis of characteristic clinical and pathological findings. The definitive etiological diagnosis by virus isolation is time consuming, expensive and elusive. Isolation of the virus in cell cultures is rather difficult since it has no characteristic cytopathic effect (CPE). Furthermore, many strains have no CPE at all. Due to these uncertainties, virus isolation trials are generally supported by additional tests (Radostits & Littlejohns 1988).