Twelve (Experiment I) and four (Experiment II) multiparous dairy cows seronegative to pestivirus were selected and randomly assigned to either a control group which did not become infected or a treatment group in which all cows became infected following intranasal inoculation 9 days before AI. The experimental induction of infection was carried out with 2 ml of non-cytopathic pestivirus (BVD virus) suspension containing 5 log10 TCID50/ml (Experiment I) and 4.5 log10 TCID50/ml (Experiment II). In both experiments, the cows were superovulated on day 10±2 of the cycle using the standard procedures. The cows in Experiment I were artificially inseminated at 12 and 24 h after the onset of estrus and a non-surgical ova/embryo collection was performed 7 days after AI. In Experiment II, the cows were slaughtered on day 8 after superovulation-induced estrus and the ovaries submitted for gross and histopahological examination including immunohistochemistry. Mean (±SE) number of ovulatory sized follicles on day of AI and corpora lutea palpated on day 7 after AI were significantly (p