Malignant catarrhal fever virus was not isolated from samples of fetal membranes or fluid collected from 93 calving wildebeest (Connochaetes taurinus) in Kenya Maasailand. Cell-free strains of malignant catarrhal fever virus were very rapidly inactivated when exposed to the sun under field conditions, at least 3.0 log10 units/25 microliter being lost per hour at midday. It is suggested that wildebeest fetal membranes and fluids act as visual markers for areas of pasture which are particularly heavily contaminated with malignant catarrhal fever virus in oculonasal secretions of wildebeest calves. It is possible that starting to graze cattle one to two hours later each morning may be a useful measure for helping to protect cattle from malignant catarrhal fever in areas where they are forced to share pastures with calving wildebeest.