Paraffin sections from various organs of sheep fetuses following transplacental infection with non-cytopathogenic (ncp) bovine viral diarrhoea virus (BVDV) or cytopathogenic (cp) BVDV were stained immunohistochemically with BVDV-specific monoclonal antibodies. Comparison of the distribution of viral antigen in sections from fetuses of experiment A revealed that in organs such as parotid, thyroid, thymus, lung, spleen, kidney, liver and skin from 20 days post inoculation (p.i.) onwards numerous antigen-containing cells were present. In organs of fetuses infected with cp BVDV, however, antigen-positive cells were only detectable until days 10 and 14 p.i. These findings suggest that the ncp BVDV used in experiment A replicated considerably faster and more efficient than the cp BVDV used in experiment B and that the two virus biotypes differ considerably concerning their tropism for fetal ovine organs.