Between November 1977 and June 1978, 280 beef bulls for sale at an auction in central Oklahoma, USA, were examined for Tritrichomonas foetus infection by a swab culture technique. Over-all 7.8% were infected, including 7.8, 11.6 and 14.6% of 4-, 5- and 6-year-olds, respectively. The prevalence in Brahmans was 14.6%, in Angus 10.3% and in Hereford bulls 5.6%. It is estimated that in Oklahoma bovine trichomoniasis, by reducing the calving rate, causes an annual economic loss of $5 million; this becomes $7 million if estimates of related production costs are included.